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• Insert a row and avoiding race condition (PHP/MySQL)

  - by justkevin

  I'm working on a multiplayer game which has a lobby-like area where players select "sectors" to enter. The lobby gateway is powered by PHP, while actual gameplay is handled by one or more Java servers. The datastore is MySQL. The happy path: A player chooses a sector and tells the lobby he'd like to enter. The lobby checks whether this is okay, including checking whether there are too many players in the sector (compares the entry count in sector assignments for that sector against the sector's max_players value). The player is added to the sector_assignments table pairing him with the sector. The player client receives a passkey that will let him connect to the appropriate game server. The race condition: If two players request access to the same sector at close to same time, I can envision a case where they are both added because there was one space free when their check was started and max players gets exceeded. Is the best solution LOCK TABLE on sector_assignments? Is there another option?

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• Updating multiple rows with an array

  - by Copephobia

  I have a table that holds user information. One of the columns holds the position of the user in the game they are in. When a game is being created, I need to update the positions of the users of each team. Here is an example: Game id : 7 Team 1 users : 1,2 Team 2 users : 3,4 team1_position : array(1,2) team2_position : array(13,14) What I want to do is update the user table using the array of positions in the SET area. My goal is to be able to update the users without the need for their id (I have different size game boards, so I have multiple position arrays for each board size) How can I do something like this: UPDATE user SET position='(team1_position)' WHERE game = '7' AND team = '1' I feel like it would be a waste of resources to select all the id's of each team and update them separately.

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• JQuery input hidden bug

  - by Abude

  this is the code: Jsfiddle when you clear the url filed and leave it empty the input is hidden and disappear , need to return to the input tag wit h display if the value is empty by click or tab. i have a form with inputs the url input is edited by clicking on the link double click or click next to the link that means in the div area when it's done editing it converts the text to link the Problem: when you leave the input empty it make the attribute of the code and the input attribute hidden so no info is show neither can type an info. how can i make if that input with the id url0/url1 is empty to return to the input option to make it visible and can type?

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• Jquery plugin for getting changes in textarea and sending them to server

  - by user763410

  I am getting a file "abc.txt" from server and dispaying it in a text area for editing. <div id="filecontents"> <textarea> CONTENTS OF FILE LARGER THAN 10KB </textarea> </div> The contents of the file are potentially large. The user will edit the textarea and add/delete text from any part(not just the end). I want to send ONLY the changes to the server for patching. How do I accomplish this?. Is there a javascript version of the popular linux command(diff). John Resig's diff code may not work as, for me, it will involve additional parsing on server side. Thanks!

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• How can I make a TextArea 100% width without overflowing when padding is present in CSS?

  - by spoon16

  I have the following HTML snippet being rendered. <div style="display: block;" id="rulesformitem" class="formitem"> <label for="rules" id="ruleslabel">Rules:</label> <textarea cols="2" rows="10" id="rules"/> </div> This is my CSS: textarea { border:1px solid #999999; width:100%; margin:5px 0; padding:3px; } Is the problem is that the text area ends up being 8px wider (2px for border + 6px for padding) than the parent. Is there a way to continue to use border and padding but constrain the total size of the textarea to the width of the parent?

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• IIS Strategies for Accessing Secured Network Resources

  - by ErikE

  Problem: A user connects to a service on a machine, such as an IIS web site or a SQL Server database. The site or the database need to gain access to network resources such as file shares (the most common) or a database on a different server. Permission is denied. This is because the user the service is running under doesn't have network permissions in the first place, or if it does, it doesn't have rights to access the remote resource. I keep running into this problem over and over again and am tired of not having a really solid way of handling it. Here are some workarounds I'm aware of: Run IIS as a custom-created domain user who is granted high permissions If permissions are granted one file share at a time, then every time I want to read from a new share, I would have to ask a network admin to add it for me. Eventually, with many web sites reading from many shares, it is going to get really complicated. If permissions are just opened up wide for the user to access any file shares in our domain, then this seems like an unnecessary security surface area to present. This also applies to all the sites running on IIS, rather than just the selected site or virtual directory that needs the access, a further surface area problem. Still use the IUSR account but give it network permissions and set up the same user name on the remote resource (not a domain user, a local user) This also has its problems. For example, there's a file share I am using that I have full rights to for sharing, but I can't log in to the machine. So I have to find the right admin and ask him to do it for me. Any time something has to change, it's another request to an admin. Allow IIS users to connect as anonymous, but set the account used for anonymous access to a high-privilege one This is even worse than giving the IIS IUSR full privileges, because it means my web site can't use any kind of security in the first place. Connect using Kerberos, then delegate This sounds good in principle but has all sorts of problems. First of all, if you're using virtual web sites where the domain name you connect to the site with is not the base machine name (as we do frequently), then you have to set up a Service Principal Name on the webserver using Microsoft's SetSPN utility. It's complicated and apparently prone to errors. Also, you have to ask your network/domain admin to change security policy for both the web server and the domain account so they are "trusted for delegation." If you don't get everything perfectly right, suddenly your intended Kerberos authentication is NTLM instead, and you can only impersonate rather than delegate, and thus no reaching out over the network as the user. Also, this method can be problematic because sometimes you need the web site or database to have permissions that the connecting user doesn't have. Create a service or COM+ application that fetches the resource for the web site Services and COM+ packages are run with their own set of credentials. Running as a high-privilege user is okay since they can do their own security and deny requests that are not legitimate, putting control in the hands of the application developer instead of the network admin. Problems: I am using a COM+ package that does exactly this on Windows Server 2000 to deliver highly sensitive images to a secured web application. I tried moving the web site to Windows Server 2003 and was suddenly denied permission to instantiate the COM+ object, very likely registry permissions. I trolled around quite a bit and did not solve the problem, partly because I was reluctant to give the IUSR account full registry permissions. That seems like the same bad practice as just running IIS as a high-privilege user. Note: This is actually really simple. In a programming language of your choice, you create a class with a function that returns an instance of the object you want (an ADODB.Connection, for example), and build a dll, which you register as a COM+ object. In your web server-side code, you create an instance of the class and use the function, and since it is running under a different security context, calls to network resources work. Map drive letters to shares This could theoretically work, but in my mind it's not really a good long-term strategy. Even though mappings can be created with specific credentials, and this can be done by others than a network admin, this also is going to mean that there are either way too many shared drives (small granularity) or too much permission is granted to entire file servers (large granularity). Also, I haven't figured out how to map a drive so that the IUSR gets the drives. Mapping a drive is for the current user, I don't know the IUSR account password to log in as it and create the mappings. Move the resources local to the web server/database There are times when I've done this, especially with Access databases. Does the database have to live out on the file share? Sometimes, it was just easiest to move the database to the web server or to the SQL database server (so the linked server to it would work). But I don't think this is a great all-around solution, either. And it won't work when the resource is a service rather than a file. Move the service to the final web server/database I suppose I could run a web server on my SQL Server database, so the web site can connect to it using impersonation and make me happy. But do we really want random extra web servers on our database servers just so this is possible? No. Virtual directories in IIS I know that virtual directories can help make remote resources look as though they are local, and this supports using custom credentials for each virtual directory. I haven't been able to come up with, yet, how this would solve the problem for system calls. Users could reach file shares directly, but this won't help, say, classic ASP code access resources. I could use a URL instead of a file path to read remote data files in a web page, but this isn't going to help me make a connection to an Access database, a SQL server database, or any other resource that uses a connection library rather than being able to just read all the bytes and work with them. I wish there was some kind of "service tunnel" that I could create. Think about how a VPN makes remote resources look like they are local. With a richer aliasing mechanism, perhaps code-based, why couldn't even database connections occur under a defined security context? Why not a special Windows component that lets you specify, per user, what resources are available and what alternate credentials are used for the connection? File shares, databases, web sites, you name it. I guess I'm almost talking about a specialized local proxy server. Anyway, so there's my list. I may update it if I think of more. Does anyone have any ideas for me? My current problem today is, yet again, I need a web site to connect to an Access database on a file share. Here we go again...

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• IIS Strategies for Accessing Secured Network Resources

  - by Emtucifor

  Problem: A user connects to a service on a machine, such as an IIS web site or a SQL Server database. The site or the database need to gain access to network resources such as file shares (the most common) or a database on a different server. Permission is denied. This is because the user the service is running as doesn't have network permissions in the first place, or if it does, it doesn't have rights to access the remote resource. I keep running into this problem over and over again and am tired of not having a really solid way of handling it. Here are some workarounds I'm aware of: Run IIS as a custom-created domain user who is granted high permissions If permissions are granted one file share at a time, then every time I want to read from a new share, I would have to ask a network admin to add it for me. Eventually, with many web sites reading from many shares, it is going to get really complicated. If permissions are just opened up wide for the user to access any file shares in our domain, then this seems like an unnecessary security surface area to present. This also applies to all the sites running on IIS, rather than just the selected site or virtual directory that needs the access, a further surface area problem. Still use the IUSR account but give it network permissions and set up the same user name on the remote resource (not a domain user, a local user) This also has its problems. For example, there's a file share I am using that I have full rights to for sharing, but I can't log in to the machine. So I have to find the right admin and ask him to do it for me. Any time something has to change, it's another request to an admin. Allow IIS users to connect as anonymous, but set the account used for anonymous access to a high-privilege one This is even worse than giving the IIS IUSR full privileges, because it means my web site can't use any kind of security in the first place. Connect using Kerberos, then delegate This sounds good in principle but has all sorts of problems. First of all, if you're using virtual web sites where the domain name you connect to the site with is not the base machine name (as we do frequently), then you have to set up a Service Principal Name on the webserver using Microsoft's SetSPN utility. It's complicated and apparently prone to errors. Also, you have to ask your network/domain admin to change security policy for the web server so it is "trusted for delegation." If you don't get everything perfectly right, suddenly your intended Kerberos authentication is NTLM instead, and you can only impersonate rather than delegate, and thus no reaching out over the network as the user. Also, this method can be problematic because sometimes you need the web site or database to have permissions that the connecting user doesn't have. Create a service or COM+ application that fetches the resource for the web site Services and COM+ packages are run with their own set of credentials. Running as a high-privilege user is okay since they can do their own security and deny requests that are not legitimate, putting control in the hands of the application developer instead of the network admin. Problems: I am using a COM+ package that does exactly this on Windows Server 2000 to deliver highly sensitive images to a secured web application. I tried moving the web site to Windows Server 2003 and was suddenly denied permission to instantiate the COM+ object, very likely registry permissions. I trolled around quite a bit and did not solve the problem, partly because I was reluctant to give the IUSR account full registry permissions. That seems like the same bad practice as just running IIS as a high-privilege user. Note: This is actually really simple. In a programming language of your choice, you create a class with a function that returns an instance of the object you want (an ADODB.Connection, for example), and build a dll, which you register as a COM+ object. In your web server-side code, you create an instance of the class and use the function, and since it is running under a different security context, calls to network resources work. Map drive letters to shares This could theoretically work, but in my mind it's not really a good long-term strategy. Even though mappings can be created with specific credentials, and this can be done by others than a network admin, this also is going to mean that there are either way too many shared drives (small granularity) or too much permission is granted to entire file servers (large granularity). Also, I haven't figured out how to map a drive so that the IUSR gets the drives. Mapping a drive is for the current user, I don't know the IUSR account password to log in as it and create the mappings. Move the resources local to the web server/database There are times when I've done this, especially with Access databases. Does the database have to live out on the file share? Sometimes, it was just easiest to move the database to the web server or to the SQL database server (so the linked server to it would work). But I don't think this is a great all-around solution, either. And it won't work when the resource is a service rather than a file. Move the service to the final web server/database I suppose I could run a web server on my SQL Server database, so the web site can connect to it using impersonation and make me happy. But do we really want random extra web servers on our database servers just so this is possible? No. Virtual directories in IIS I know that virtual directories can help make remote resources look as though they are local, and this supports using custom credentials for each virtual directory. I haven't been able to come up with, yet, how this would solve the problem for system calls. Users could reach file shares directly, but this won't help, say, classic ASP code access resources. I could use a URL instead of a file path to read remote data files in a web page, but this isn't going to help me make a connection to an Access database, a SQL server database, or any other resource that uses a connection library rather than being able to just read all the bytes and work with them. I wish there was some kind of "service tunnel" that I could create. Think about how a VPN makes remote resources look like they are local. With a richer aliasing mechanism, perhaps code-based, why couldn't even database connections occur under a defined security context? Why not a special Windows component that lets you specify, per user, what resources are available and what alternate credentials are used for the connection? File shares, databases, web sites, you name it. I guess I'm almost talking about a specialized local proxy server. Anyway, so there's my list. I may update it if I think of more. Does anyone have any ideas for me? My current problem today is, yet again, I need a web site to connect to an Access database on a file share. Here we go again...

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• How to run a DHCP service on Windows 7 Home

  - by Joshua Lim

  I'm trying to setup a DHCP server on Windows 7 Home, tried using a couple of freeware which I found on the Internet but none seemed to work. What I did: On the Windows 7 machine which I install the DHCP Server with the range 192.168.1.12-192.168.1.256. I set the Gigabit Ethernet adapter to a static IP address of 192.168.1.11 and subnet mask of 255.255.255.0. When I did an IP config, it showed. Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : Description . . . . . . . . . . . : Broadcom NetLink (TM) Gigabit Ethernet Physical Address. . . . . . . . . : 8C-73-6E-75-A7-56 DHCP Enabled. . . . . . . . . . . : No Autoconfiguration Enabled . . . . : Yes Link-local IPv6 Address . . . . . : fe80::196d:b6bb:8f93:2555%12(Preferred) IPv4 Address. . . . . . . . . . . : 192.168.1.11(Preferred) Subnet Mask . . . . . . . . . . . : 255.255.255.0 Default Gateway . . . . . . . . . : DNS Servers . . . . . . . . . . . : fec0:0:0:ffff::1%1 fec0:0:0:ffff::2%1 fec0:0:0:ffff::3%1 NetBIOS over Tcpip. . . . . . . . : Enabled I connected another Window 7 machine to the "DHCP server" using a cross cable and set network adapter on that machine to automatically detect IP address. The client fails to acquire the correct IP address from the DHCP server and showed the autoconfigured IPv4 address instead. Here's the information returned by config /all on the client machine. Ethernet adapter Local Area Connection: Connection-specific DNS Suffix . : Description . . . . . . . . . . . : Atheros AR8152/8158 PCI-E Fast Ethernet Controller (NDIS 6.20) Physical Address. . . . . . . . . : 54-04-A6-40-96-4B DHCP Enabled. . . . . . . . . . . : Yes Autoconfiguration Enabled . . . . : Yes Link-local IPv6 Address . . . . . : fe80::4885:4082:5572:5a85%12(Preferred) Autoconfiguration IPv4 Address. . : 169.254.90.133(Preferred) Subnet Mask . . . . . . . . . . . : 255.255.0.0 Default Gateway . . . . . . . . . : DHCPv6 IAID . . . . . . . . . . . : 341050534 DHCPv6 Client DUID. . . . . . . . : 00-01-00-01-17-54-78-12-00-08-CA-46-4C-5A DNS Servers . . . . . . . . . . . : fec0:0:0:ffff::1%1 fec0:0:0:ffff::2%1 fec0:0:0:ffff::3%1 NetBIOS over Tcpip. . . . . . . . : Enabled DHCP client are running on both machines. I've tried many times but failed. Googling also returned no useful information for my scenario. Have I missed out any step? Thanks.

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• SQL Server 2012 - AlwaysOn

  - by Claus Jandausch

  Ich war nicht nur irritiert, ich war sogar regelrecht schockiert - und für einen kurzen Moment sprachlos (was nur selten der Fall ist). Gerade eben hatte mich jemand gefragt "Wann Oracle denn etwas Vergleichbares wie AlwaysOn bieten würde - und ob überhaupt?" War ich hier im falschen Film gelandet? Ich konnte nicht anders, als meinen Unmut kundzutun und zu erklären, dass die Fragestellung normalerweise anders herum läuft. Zugegeben - es mag vielleicht strittige Punkte geben im Vergleich zwischen Oracle und SQL Server - bei denen nicht unbedingt immer Oracle die Nase vorn haben muss - aber das Thema Clustering für Hochverfügbarkeit (HA), Disaster Recovery (DR) und Skalierbarkeit gehört mit Sicherheit nicht dazu. Dieses Erlebnis hakte ich am Nachgang als Einzelfall ab, der so nie wieder vorkommen würde. Bis ich kurz darauf eines Besseren belehrt wurde und genau die selbe Frage erneut zu hören bekam. Diesmal sogar im Exadata-Umfeld und einem Oracle Stretch Cluster. Einmal ist keinmal, doch zweimal ist einmal zu viel... Getreu diesem alten Motto war mir klar, dass man das so nicht länger stehen lassen konnte. Ich habe keine Ahnung, wie die Microsoft Marketing Abteilung es geschafft hat, unter dem AlwaysOn Brading eine innovative Technologie vermuten zu lassen - aber sie hat ihren Job scheinbar gut gemacht. Doch abgesehen von einem guten Marketing, stellt sich natürlich die Frage, was wirklich dahinter steckt und wie sich das Ganze mit Oracle vergleichen lässt - und ob überhaupt? Damit wären wir wieder bei der ursprünglichen Frage angelangt.  So viel zum Hintergrund dieses Blogbeitrags - von meiner Antwort handelt der restliche Blog. "Windows was the God ..." Um den wahren Unterschied zwischen Oracle und Microsoft verstehen zu können, muss man zunächst das bedeutendste Microsoft Dogma kennen. Es lässt sich schlicht und einfach auf den Punkt bringen: "Alles muss auf Windows basieren." Die Überschrift dieses Absatzes ist kein von mir erfundener Ausspruch, sondern ein Zitat. Konkret stammt es aus einem längeren Artikel von Kurt Eichenwald in der Vanity Fair aus dem August 2012. Er lautet Microsoft's Lost Decade und sei jedem ans Herz gelegt, der die "Microsoft-Maschinerie" unter Steve Ballmer und einige ihrer Kuriositäten besser verstehen möchte. "YOU TALKING TO ME?" Microsoft C.E.O. Steve Ballmer bei seiner Keynote auf der 2012 International Consumer Electronics Show in Las Vegas am 9. Januar   Manche Dinge in diesem Artikel mögen überspitzt dargestellt erscheinen - sind sie aber nicht. Vieles davon kannte ich bereits aus eigener Erfahrung und kann es nur bestätigen. Anderes hat sich mir erst so richtig erschlossen. Insbesondere die folgenden Passagen führten zum Aha-Erlebnis: “Windows was the god—everything had to work with Windows,” said Stone... “Every little thing you want to write has to build off of Windows (or other existing roducts),” one software engineer said. “It can be very confusing, …” Ich habe immer schon darauf hingewiesen, dass in einem SQL Server Failover Cluster die Microsoft Datenbank eigentlich nichts Nenneswertes zum Geschehen beiträgt, sondern sich voll und ganz auf das Windows Betriebssystem verlässt. Deshalb muss man auch die Windows Server Enterprise Edition installieren, soll ein Failover Cluster für den SQL Server eingerichtet werden. Denn hier werden die Cluster Services geliefert - nicht mit dem SQL Server. Er ist nur lediglich ein weiteres Server Produkt, für das Windows in Ausfallszenarien genutzt werden kann - so wie Microsoft Exchange beispielsweise, oder Microsoft SharePoint, oder irgendein anderes Server Produkt das auf Windows gehostet wird. Auch Oracle kann damit genutzt werden. Das Stichwort lautet hier: Oracle Failsafe. Nur - warum sollte man das tun, wenn gleichzeitig eine überlegene Technologie wie die Oracle Real Application Clusters (RAC) zur Verfügung steht, die dann auch keine Windows Enterprise Edition voraussetzen, da Oracle die eigene Clusterware liefert. Welche darüber hinaus für kürzere Failover-Zeiten sorgt, da diese Cluster-Technologie Datenbank-integriert ist und sich nicht auf "Dritte" verlässt. Wenn man sich also schon keine technischen Vorteile mit einem SQL Server Failover Cluster erkauft, sondern zusätzlich noch versteckte Lizenzkosten durch die Lizenzierung der Windows Server Enterprise Edition einhandelt, warum hat Microsoft dann in den vergangenen Jahren seit SQL Server 2000 nicht ebenfalls an einer neuen und innovativen Lösung gearbeitet, die mit Oracle RAC mithalten kann? Entwickler hat Microsoft genügend? Am Geld kann es auch nicht liegen? Lesen Sie einfach noch einmal die beiden obenstehenden Zitate und sie werden den Grund verstehen. Anders lässt es sich ja auch gar nicht mehr erklären, dass AlwaysOn aus zwei unterschiedlichen Technologien besteht, die beide jedoch wiederum auf dem Windows Server Failover Clustering (WSFC) basieren. Denn daraus ergeben sich klare Nachteile - aber dazu später mehr. Um AlwaysOn zu verstehen, sollte man sich zunächst kurz in Erinnerung rufen, was Microsoft bisher an HA/DR (High Availability/Desaster Recovery) Lösungen für SQL Server zur Verfügung gestellt hat. Replikation Basiert auf logischer Replikation und Pubisher/Subscriber Architektur Transactional Replication Merge Replication Snapshot Replication Microsoft's Replikation ist vergleichbar mit Oracle GoldenGate. Oracle GoldenGate stellt jedoch die umfassendere Technologie dar und bietet High Performance. Log Shipping Microsoft's Log Shipping stellt eine einfache Technologie dar, die vergleichbar ist mit Oracle Managed Recovery in Oracle Version 7. Das Log Shipping besitzt folgende Merkmale: Transaction Log Backups werden von Primary nach Secondary/ies geschickt Einarbeitung (z.B. Restore) auf jedem Secondary individuell Optionale dritte Server Instanz (Monitor Server) für Überwachung und Alarm Log Restore Unterbrechung möglich für Read-Only Modus (Secondary) Keine Unterstützung von Automatic Failover Database Mirroring Microsoft's Database Mirroring wurde verfügbar mit SQL Server 2005, sah aus wie Oracle Data Guard in Oracle 9i, war funktional jedoch nicht so umfassend. Für ein HA/DR Paar besteht eine 1:1 Beziehung, um die produktive Datenbank (Principle DB) abzusichern. Auf der Standby Datenbank (Mirrored DB) werden alle Insert-, Update- und Delete-Operationen nachgezogen. Modi Synchron (High-Safety Modus) Asynchron (High-Performance Modus) Automatic Failover Unterstützt im High-Safety Modus (synchron) Witness Server vorausgesetzt     Zur Frage der Kontinuität Es stellt sich die Frage, wie es um diesen Technologien nun im Zusammenhang mit SQL Server 2012 bestellt ist. Unter Fanfaren seinerzeit eingeführt, war Database Mirroring das erklärte Mittel der Wahl. Ich bin kein Produkt Manager bei Microsoft und kann hierzu nur meine Meinung äußern, aber zieht man den SQL AlwaysOn Team Blog heran, so sieht es nicht gut aus für das Database Mirroring - zumindest nicht langfristig. "Does AlwaysOn Availability Group replace Database Mirroring going forward?” “The short answer is we recommend that you migrate from the mirroring configuration or even mirroring and log shipping configuration to using Availability Group. Database Mirroring will still be available in the Denali release but will be phased out over subsequent releases. Log Shipping will continue to be available in future releases.” Damit wären wir endlich beim eigentlichen Thema angelangt. Was ist eine sogenannte Availability Group und was genau hat es mit der vielversprechend klingenden Bezeichnung AlwaysOn auf sich?   SQL Server 2012 - AlwaysOn Zwei HA-Features verstekcne sich hinter dem “AlwaysOn”-Branding. Einmal das AlwaysOn Failover Clustering aka SQL Server Failover Cluster Instances (FCI) - zum Anderen die AlwaysOn Availability Groups. Failover Cluster Instances (FCI) Entspricht ungefähr dem Stretch Cluster Konzept von Oracle Setzt auf Windows Server Failover Clustering (WSFC) auf Bietet HA auf Instanz-Ebene AlwaysOn Availability Groups (Verfügbarkeitsgruppen) Ähnlich der Idee von Consistency Groups, wie in Storage-Level Replikations-Software von z.B. EMC SRDF Abhängigkeiten zu Windows Server Failover Clustering (WSFC) Bietet HA auf Datenbank-Ebene   Hinweis: Verwechseln Sie nicht eine SQL Server Datenbank mit einer Oracle Datenbank. Und auch nicht eine Oracle Instanz mit einer SQL Server Instanz. Die gleichen Begriffe haben hier eine andere Bedeutung - nicht selten ein Grund, weshalb Oracle- und Microsoft DBAs schnell aneinander vorbei reden. Denken Sie bei einer SQL Server Datenbank eher an ein Oracle Schema, das kommt der Sache näher. So etwas wie die SQL Server Northwind Datenbank ist vergleichbar mit dem Oracle Scott Schema. Wenn Sie die genauen Unterschiede kennen möchten, finden Sie eine detaillierte Beschreibung in meinem Buch "Oracle10g Release 2 für Windows und .NET", erhältich bei Lehmanns, Amazon, etc.   Windows Server Failover Clustering (WSFC) Wie man sieht, basieren beide AlwaysOn Technologien wiederum auf dem Windows Server Failover Clustering (WSFC), um einerseits Hochverfügbarkeit auf Ebene der Instanz zu gewährleisten und andererseits auf der Datenbank-Ebene. Deshalb nun eine kurze Beschreibung der WSFC. Die WSFC sind ein mit dem Windows Betriebssystem geliefertes Infrastruktur-Feature, um HA für Server Anwendungen, wie Microsoft Exchange, SharePoint, SQL Server, etc. zu bieten. So wie jeder andere Cluster, besteht ein WSFC Cluster aus einer Gruppe unabhängiger Server, die zusammenarbeiten, um die Verfügbarkeit einer Applikation oder eines Service zu erhöhen. Falls ein Cluster-Knoten oder -Service ausfällt, kann der auf diesem Knoten bisher gehostete Service automatisch oder manuell auf einen anderen im Cluster verfügbaren Knoten transferriert werden - was allgemein als Failover bekannt ist. Unter SQL Server 2012 verwenden sowohl die AlwaysOn Avalability Groups, als auch die AlwaysOn Failover Cluster Instances die WSFC als Plattformtechnologie, um Komponenten als WSFC Cluster-Ressourcen zu registrieren. Verwandte Ressourcen werden in eine Ressource Group zusammengefasst, die in Abhängigkeit zu anderen WSFC Cluster-Ressourcen gebracht werden kann. Der WSFC Cluster Service kann jetzt die Notwendigkeit zum Neustart der SQL Server Instanz erfassen oder einen automatischen Failover zu einem anderen Server-Knoten im WSFC Cluster auslösen.   Failover Cluster Instances (FCI) Eine SQL Server Failover Cluster Instanz (FCI) ist eine einzelne SQL Server Instanz, die in einem Failover Cluster betrieben wird, der aus mehreren Windows Server Failover Clustering (WSFC) Knoten besteht und so HA (High Availability) auf Ebene der Instanz bietet. Unter Verwendung von Multi-Subnet FCI kann auch Remote DR (Disaster Recovery) unterstützt werden. Eine weitere Option für Remote DR besteht darin, eine unter FCI gehostete Datenbank in einer Availability Group zu betreiben. Hierzu später mehr. FCI und WSFC Basis FCI, das für lokale Hochverfügbarkeit der Instanzen genutzt wird, ähnelt der veralteten Architektur eines kalten Cluster (Aktiv-Passiv). Unter SQL Server 2008 wurde diese Technologie SQL Server 2008 Failover Clustering genannt. Sie nutzte den Windows Server Failover Cluster. In SQL Server 2012 hat Microsoft diese Basistechnologie unter der Bezeichnung AlwaysOn zusammengefasst. Es handelt sich aber nach wie vor um die klassische Aktiv-Passiv-Konfiguration. Der Ablauf im Failover-Fall ist wie folgt: Solange kein Hardware-oder System-Fehler auftritt, werden alle Dirty Pages im Buffer Cache auf Platte geschrieben Alle entsprechenden SQL Server Services (Dienste) in der Ressource Gruppe werden auf dem aktiven Knoten gestoppt Die Ownership der Ressource Gruppe wird auf einen anderen Knoten der FCI transferriert Der neue Owner (Besitzer) der Ressource Gruppe startet seine SQL Server Services (Dienste) Die Connection-Anforderungen einer Client-Applikation werden automatisch auf den neuen aktiven Knoten mit dem selben Virtuellen Network Namen (VNN) umgeleitet Abhängig vom Zeitpunkt des letzten Checkpoints, kann die Anzahl der Dirty Pages im Buffer Cache, die noch auf Platte geschrieben werden müssen, zu unvorhersehbar langen Failover-Zeiten führen. Um diese Anzahl zu drosseln, besitzt der SQL Server 2012 eine neue Fähigkeit, die Indirect Checkpoints genannt wird. Indirect Checkpoints ähnelt dem Fast-Start MTTR Target Feature der Oracle Datenbank, das bereits mit Oracle9i verfügbar war.   SQL Server Multi-Subnet Clustering Ein SQL Server Multi-Subnet Failover Cluster entspricht vom Konzept her einem Oracle RAC Stretch Cluster. Doch dies ist nur auf den ersten Blick der Fall. Im Gegensatz zu RAC ist in einem lokalen SQL Server Failover Cluster jeweils nur ein Knoten aktiv für eine Datenbank. Für die Datenreplikation zwischen geografisch entfernten Sites verlässt sich Microsoft auf 3rd Party Lösungen für das Storage Mirroring.     Die Verbesserung dieses Szenario mit einer SQL Server 2012 Implementierung besteht schlicht darin, dass eine VLAN-Konfiguration (Virtual Local Area Network) nun nicht mehr benötigt wird, so wie dies bisher der Fall war. Das folgende Diagramm stellt dar, wie der Ablauf mit SQL Server 2012 gehandhabt wird. In Site A und Site B wird HA jeweils durch einen lokalen Aktiv-Passiv-Cluster sichergestellt.     Besondere Aufmerksamkeit muss hier der Konfiguration und dem Tuning geschenkt werden, da ansonsten völlig inakzeptable Failover-Zeiten resultieren. Dies liegt darin begründet, weil die Downtime auf Client-Seite nun nicht mehr nur von der reinen Failover-Zeit abhängt, sondern zusätzlich von der Dauer der DNS Replikation zwischen den DNS Servern. (Rufen Sie sich in Erinnerung, dass wir gerade von Multi-Subnet Clustering sprechen). Außerdem ist zu berücksichtigen, wie schnell die Clients die aktualisierten DNS Informationen abfragen. Spezielle Konfigurationen für Node Heartbeat, HostRecordTTL (Host Record Time-to-Live) und Intersite Replication Frequeny für Active Directory Sites und Services werden notwendig. Default TTL für Windows Server 2008 R2: 20 Minuten Empfohlene Einstellung: 1 Minute DNS Update Replication Frequency in Windows Umgebung: 180 Minuten Empfohlene Einstellung: 15 Minuten (minimaler Wert)   Betrachtet man diese Werte, muss man feststellen, dass selbst eine optimale Konfiguration die rigiden SLAs (Service Level Agreements) heutiger geschäftskritischer Anwendungen für HA und DR nicht erfüllen kann. Denn dies impliziert eine auf der Client-Seite erlebte Failover-Zeit von insgesamt 16 Minuten. Hierzu ein Auszug aus der SQL Server 2012 Online Dokumentation: Cons: If a cross-subnet failover occurs, the client recovery time could be 15 minutes or longer, depending on your HostRecordTTL setting and the setting of your cross-site DNS/AD replication schedule.    Wir sind hier an einem Punkt unserer Überlegungen angelangt, an dem sich erklärt, weshalb ich zuvor das "Windows was the God ..." Zitat verwendet habe. Die unbedingte Abhängigkeit zu Windows wird zunehmend zum Problem, da sie die Komplexität einer Microsoft-basierenden Lösung erhöht, anstelle sie zu reduzieren. Und Komplexität ist das Letzte, was sich CIOs heutzutage wünschen.  Zur Ehrenrettung des SQL Server 2012 und AlwaysOn muss man sagen, dass derart lange Failover-Zeiten kein unbedingtes "Muss" darstellen, sondern ein "Kann". Doch auch ein "Kann" kann im unpassenden Moment unvorhersehbare und kostspielige Folgen haben. Die Unabsehbarkeit ist wiederum Ursache vieler an der Implementierung beteiligten Komponenten und deren Abhängigkeiten, wie beispielsweise drei Cluster-Lösungen (zwei von Microsoft, eine 3rd Party Lösung). Wie man die Sache auch dreht und wendet, kommt man an diesem Fakt also nicht vorbei - ganz unabhängig von der Dauer einer Downtime oder Failover-Zeiten. Im Gegensatz zu AlwaysOn und der hier vorgestellten Version eines Stretch-Clusters, vermeidet eine entsprechende Oracle Implementierung eine derartige Komplexität, hervorgerufen duch multiple Abhängigkeiten. Den Unterschied machen Datenbank-integrierte Mechanismen, wie Fast Application Notification (FAN) und Fast Connection Failover (FCF). Für Oracle MAA Konfigurationen (Maximum Availability Architecture) sind Inter-Site Failover-Zeiten im Bereich von Sekunden keine Seltenheit. Wenn Sie dem Link zur Oracle MAA folgen, finden Sie außerdem eine Reihe an Customer Case Studies. Auch dies ist ein wichtiges Unterscheidungsmerkmal zu AlwaysOn, denn die Oracle Technologie hat sich bereits zigfach in höchst kritischen Umgebungen bewährt.   Availability Groups (Verfügbarkeitsgruppen) Die sogenannten Availability Groups (Verfügbarkeitsgruppen) sind - neben FCI - der weitere Baustein von AlwaysOn.   Hinweis: Bevor wir uns näher damit beschäftigen, sollten Sie sich noch einmal ins Gedächtnis rufen, dass eine SQL Server Datenbank nicht die gleiche Bedeutung besitzt, wie eine Oracle Datenbank, sondern eher einem Oracle Schema entspricht. So etwas wie die SQL Server Northwind Datenbank ist vergleichbar mit dem Oracle Scott Schema.   Eine Verfügbarkeitsgruppe setzt sich zusammen aus einem Set mehrerer Benutzer-Datenbanken, die im Falle eines Failover gemeinsam als Gruppe behandelt werden. Eine Verfügbarkeitsgruppe unterstützt ein Set an primären Datenbanken (primäres Replikat) und einem bis vier Sets von entsprechenden sekundären Datenbanken (sekundäre Replikate).       Es können jedoch nicht alle SQL Server Datenbanken einer AlwaysOn Verfügbarkeitsgruppe zugeordnet werden. Der SQL Server Spezialist Michael Otey zählt in seinem SQL Server Pro Artikel folgende Anforderungen auf: Verfügbarkeitsgruppen müssen mit Benutzer-Datenbanken erstellt werden. System-Datenbanken können nicht verwendet werden Die Datenbanken müssen sich im Read-Write Modus befinden. Read-Only Datenbanken werden nicht unterstützt Die Datenbanken in einer Verfügbarkeitsgruppe müssen Multiuser Datenbanken sein Sie dürfen nicht das AUTO_CLOSE Feature verwenden Sie müssen das Full Recovery Modell nutzen und es muss ein vollständiges Backup vorhanden sein Eine gegebene Datenbank kann sich nur in einer einzigen Verfügbarkeitsgruppe befinden und diese Datenbank düerfen nicht für Database Mirroring konfiguriert sein Microsoft empfiehl außerdem, dass der Verzeichnispfad einer Datenbank auf dem primären und sekundären Server identisch sein sollte Wie man sieht, eignen sich Verfügbarkeitsgruppen nicht, um HA und DR vollständig abzubilden. Die Unterscheidung zwischen der Instanzen-Ebene (FCI) und Datenbank-Ebene (Availability Groups) ist von hoher Bedeutung. Vor kurzem wurde mir gesagt, dass man mit den Verfügbarkeitsgruppen auf Shared Storage verzichten könne und dadurch Kosten spart. So weit so gut ... Man kann natürlich eine Installation rein mit Verfügbarkeitsgruppen und ohne FCI durchführen - aber man sollte sich dann darüber bewusst sein, was man dadurch alles nicht abgesichert hat - und dies wiederum für Desaster Recovery (DR) und SLAs (Service Level Agreements) bedeutet. Kurzum, um die Kombination aus beiden AlwaysOn Produkten und der damit verbundene Komplexität kommt man wohl in der Praxis nicht herum.    Availability Groups und WSFC AlwaysOn hängt von Windows Server Failover Clustering (WSFC) ab, um die aktuellen Rollen der Verfügbarkeitsreplikate einer Verfügbarkeitsgruppe zu überwachen und zu verwalten, und darüber zu entscheiden, wie ein Failover-Ereignis die Verfügbarkeitsreplikate betrifft. Das folgende Diagramm zeigt de Beziehung zwischen Verfügbarkeitsgruppen und WSFC:   Der Verfügbarkeitsmodus ist eine Eigenschaft jedes Verfügbarkeitsreplikats. Synychron und Asynchron können also gemischt werden: Availability Modus (Verfügbarkeitsmodus) Asynchroner Commit-Modus Primäres replikat schließt Transaktionen ohne Warten auf Sekundäres Synchroner Commit-Modus Primäres Replikat wartet auf Commit von sekundärem Replikat Failover Typen Automatic Manual Forced (mit möglichem Datenverlust) Synchroner Commit-Modus Geplanter, manueller Failover ohne Datenverlust Automatischer Failover ohne Datenverlust Asynchroner Commit-Modus Nur Forced, manueller Failover mit möglichem Datenverlust   Der SQL Server kennt keinen separaten Switchover Begriff wie in Oracle Data Guard. Für SQL Server werden alle Role Transitions als Failover bezeichnet. Tatsächlich unterstützt der SQL Server keinen Switchover für asynchrone Verbindungen. Es gibt nur die Form des Forced Failover mit möglichem Datenverlust. Eine ähnliche Fähigkeit wie der Switchover unter Oracle Data Guard ist so nicht gegeben.   SQL Sever FCI mit Availability Groups (Verfügbarkeitsgruppen) Neben den Verfügbarkeitsgruppen kann eine zweite Failover-Ebene eingerichtet werden, indem SQL Server FCI (auf Shared Storage) mit WSFC implementiert wird. Ein Verfügbarkeitesreplikat kann dann auf einer Standalone Instanz gehostet werden, oder einer FCI Instanz. Zum Verständnis: Die Verfügbarkeitsgruppen selbst benötigen kein Shared Storage. Diese Kombination kann verwendet werden für lokale HA auf Ebene der Instanz und DR auf Datenbank-Ebene durch Verfügbarkeitsgruppen. Das folgende Diagramm zeigt dieses Szenario:   Achtung! Hier handelt es sich nicht um ein Pendant zu Oracle RAC plus Data Guard, auch wenn das Bild diesen Eindruck vielleicht vermitteln mag - denn alle sekundären Knoten im FCI sind rein passiv. Es existiert außerdem eine weitere und ernsthafte Einschränkung: SQL Server Failover Cluster Instanzen (FCI) unterstützen nicht das automatische AlwaysOn Failover für Verfügbarkeitsgruppen. Jedes unter FCI gehostete Verfügbarkeitsreplikat kann nur für manuelles Failover konfiguriert werden.   Lesbare Sekundäre Replikate Ein oder mehrere Verfügbarkeitsreplikate in einer Verfügbarkeitsgruppe können für den lesenden Zugriff konfiguriert werden, wenn sie als sekundäres Replikat laufen. Dies ähnelt Oracle Active Data Guard, jedoch gibt es Einschränkungen. Alle Abfragen gegen die sekundäre Datenbank werden automatisch auf das Snapshot Isolation Level abgebildet. Es handelt sich dabei um eine Versionierung der Rows. Microsoft versuchte hiermit die Oracle MVRC (Multi Version Read Consistency) nachzustellen. Tatsächlich muss man die SQL Server Snapshot Isolation eher mit Oracle Flashback vergleichen. Bei der Implementierung des Snapshot Isolation Levels handelt sich um ein nachträglich aufgesetztes Feature und nicht um einen inhärenten Teil des Datenbank-Kernels, wie im Falle Oracle. (Ich werde hierzu in Kürze einen weiteren Blogbeitrag verfassen, wenn ich mich mit der neuen SQL Server 2012 Core Lizenzierung beschäftige.) Für die Praxis entstehen aus der Abbildung auf das Snapshot Isolation Level ernsthafte Restriktionen, derer man sich für den Betrieb in der Praxis bereits vorab bewusst sein sollte: Sollte auf der primären Datenbank eine aktive Transaktion zu dem Zeitpunkt existieren, wenn ein lesbares sekundäres Replikat in die Verfügbarkeitsgruppe aufgenommen wird, werden die Row-Versionen auf der korrespondierenden sekundären Datenbank nicht sofort vollständig verfügbar sein. Eine aktive Transaktion auf dem primären Replikat muss zuerst abgeschlossen (Commit oder Rollback) und dieser Transaktions-Record auf dem sekundären Replikat verarbeitet werden. Bis dahin ist das Isolation Level Mapping auf der sekundären Datenbank unvollständig und Abfragen sind temporär geblockt. Microsoft sagt dazu: "This is needed to guarantee that row versions are available on the secondary replica before executing the query under snapshot isolation as all isolation levels are implicitly mapped to snapshot isolation." (SQL Storage Engine Blog: AlwaysOn: I just enabled Readable Secondary but my query is blocked?)  Grundlegend bedeutet dies, dass ein aktives lesbares Replikat nicht in die Verfügbarkeitsgruppe aufgenommen werden kann, ohne das primäre Replikat vorübergehend stillzulegen. Da Leseoperationen auf das Snapshot Isolation Transaction Level abgebildet werden, kann die Bereinigung von Ghost Records auf dem primären Replikat durch Transaktionen auf einem oder mehreren sekundären Replikaten geblockt werden - z.B. durch eine lang laufende Abfrage auf dem sekundären Replikat. Diese Bereinigung wird auch blockiert, wenn die Verbindung zum sekundären Replikat abbricht oder der Datenaustausch unterbrochen wird. Auch die Log Truncation wird in diesem Zustant verhindert. Wenn dieser Zustand längere Zeit anhält, empfiehlt Microsoft das sekundäre Replikat aus der Verfügbarkeitsgruppe herauszunehmen - was ein ernsthaftes Downtime-Problem darstellt. Die Read-Only Workload auf den sekundären Replikaten kann eingehende DDL Änderungen blockieren. Obwohl die Leseoperationen aufgrund der Row-Versionierung keine Shared Locks halten, führen diese Operatioen zu Sch-S Locks (Schemastabilitätssperren). DDL-Änderungen durch Redo-Operationen können dadurch blockiert werden. Falls DDL aufgrund konkurrierender Lese-Workload blockiert wird und der Schwellenwert für 'Recovery Interval' (eine SQL Server Konfigurationsoption) überschritten wird, generiert der SQL Server das Ereignis sqlserver.lock_redo_blocked, welches Microsoft zum Kill der blockierenden Leser empfiehlt. Auf die Verfügbarkeit der Anwendung wird hierbei keinerlei Rücksicht genommen.   Keine dieser Einschränkungen existiert mit Oracle Active Data Guard.   Backups auf sekundären Replikaten  Über die sekundären Replikate können Backups (BACKUP DATABASE via Transact-SQL) nur als copy-only Backups einer vollständigen Datenbank, Dateien und Dateigruppen erstellt werden. Das Erstellen inkrementeller Backups ist nicht unterstützt, was ein ernsthafter Rückstand ist gegenüber der Backup-Unterstützung physikalischer Standbys unter Oracle Data Guard. Hinweis: Ein möglicher Workaround via Snapshots, bleibt ein Workaround. Eine weitere Einschränkung dieses Features gegenüber Oracle Data Guard besteht darin, dass das Backup eines sekundären Replikats nicht ausgeführt werden kann, wenn es nicht mit dem primären Replikat kommunizieren kann. Darüber hinaus muss das sekundäre Replikat synchronisiert sein oder sich in der Synchronisation befinden, um das Beackup auf dem sekundären Replikat erstellen zu können.   Vergleich von Microsoft AlwaysOn mit der Oracle MAA Ich komme wieder zurück auf die Eingangs erwähnte, mehrfach an mich gestellte Frage "Wann denn - und ob überhaupt - Oracle etwas Vergleichbares wie AlwaysOn bieten würde?" und meine damit verbundene (kurze) Irritation. Wenn Sie diesen Blogbeitrag bis hierher gelesen haben, dann kennen Sie jetzt meine darauf gegebene Antwort. Der eine oder andere Punkt traf dabei nicht immer auf Jeden zu, was auch nicht der tiefere Sinn und Zweck meiner Antwort war. Wenn beispielsweise kein Multi-Subnet mit im Spiel ist, sind alle diesbezüglichen Kritikpunkte zunächst obsolet. Was aber nicht bedeutet, dass sie nicht bereits morgen schon wieder zum Thema werden könnten (Sag niemals "Nie"). In manch anderes Fettnäpfchen tritt man wiederum nicht unbedingt in einer Testumgebung, sondern erst im laufenden Betrieb. Erst recht nicht dann, wenn man sich potenzieller Probleme nicht bewusst ist und keine dedizierten Tests startet. Und wer AlwaysOn erfolgreich positionieren möchte, wird auch gar kein Interesse daran haben, auf mögliche Schwachstellen und den besagten Teufel im Detail aufmerksam zu machen. Das ist keine Unterstellung - es ist nur menschlich. Außerdem ist es verständlich, dass man sich in erster Linie darauf konzentriert "was geht" und "was gut läuft", anstelle auf das "was zu Problemen führen kann" oder "nicht funktioniert". Wer will schon der Miesepeter sein? Für mich selbst gesprochen, kann ich nur sagen, dass ich lieber vorab von allen möglichen Einschränkungen wissen möchte, anstelle sie dann nach einer kurzen Zeit der heilen Welt schmerzhaft am eigenen Leib erfahren zu müssen. Ich bin davon überzeugt, dass es Ihnen nicht anders geht. Nachfolgend deshalb eine Zusammenfassung all jener Punkte, die ich im Vergleich zur Oracle MAA (Maximum Availability Architecture) als unbedingt Erwähnenswert betrachte, falls man eine Evaluierung von Microsoft AlwaysOn in Betracht zieht. 1. AlwaysOn ist eine komplexe Technologie Der SQL Server AlwaysOn Stack ist zusammengesetzt aus drei verschiedenen Technlogien: Windows Server Failover Clustering (WSFC) SQL Server Failover Cluster Instances (FCI) SQL Server Availability Groups (Verfügbarkeitsgruppen) Man kann eine derartige Lösung nicht als nahtlos bezeichnen, wofür auch die vielen von Microsoft dargestellten Einschränkungen sprechen. Während sich frühere SQL Server Versionen in Richtung eigener HA/DR Technologien entwickelten (wie Database Mirroring), empfiehlt Microsoft nun die Migration. Doch weshalb dieser Schwenk? Er führt nicht zu einem konsisten und robusten Angebot an HA/DR Technologie für geschäftskritische Umgebungen.  Liegt die Antwort in meiner These begründet, nach der "Windows was the God ..." noch immer gilt und man die Nachteile der allzu engen Kopplung mit Windows nicht sehen möchte? Entscheiden Sie selbst ... 2. Failover Cluster Instanzen - Kein RAC-Pendant Die SQL Server und Windows Server Clustering Technologie basiert noch immer auf dem veralteten Aktiv-Passiv Modell und führt zu einer Verschwendung von Systemressourcen. In einer Betrachtung von lediglich zwei Knoten erschließt sich auf Anhieb noch nicht der volle Mehrwert eines Aktiv-Aktiv Clusters (wie den Real Application Clusters), wie er von Oracle bereits vor zehn Jahren entwickelt wurde. Doch kennt man die Vorzüge der Skalierbarkeit durch einfaches Hinzufügen weiterer Cluster-Knoten, die dann alle gemeinsam als ein einziges logisches System zusammenarbeiten, versteht man was hinter dem Motto "Pay-as-you-Grow" steckt. In einem Aktiv-Aktiv Cluster geht es zwar auch um Hochverfügbarkeit - und ein Failover erfolgt zudem schneller, als in einem Aktiv-Passiv Modell - aber es geht eben nicht nur darum. An dieser Stelle sei darauf hingewiesen, dass die Oracle 11g Standard Edition bereits die Nutzung von Oracle RAC bis zu vier Sockets kostenfrei beinhaltet. Möchten Sie dazu Windows nutzen, benötigen Sie keine Windows Server Enterprise Edition, da Oracle 11g die eigene Clusterware liefert. Sie kommen in den Genuss von Hochverfügbarkeit und Skalierbarkeit und können dazu die günstigere Windows Server Standard Edition nutzen. 3. SQL Server Multi-Subnet Clustering - Abhängigkeit zu 3rd Party Storage Mirroring  Die SQL Server Multi-Subnet Clustering Architektur unterstützt den Aufbau eines Stretch Clusters, basiert dabei aber auf dem Aktiv-Passiv Modell. Das eigentlich Problematische ist jedoch, dass man sich zur Absicherung der Datenbank auf 3rd Party Storage Mirroring Technologie verlässt, ohne Integration zwischen dem Windows Server Failover Clustering (WSFC) und der darunterliegenden Mirroring Technologie. Wenn nun im Cluster ein Failover auf Instanzen-Ebene erfolgt, existiert keine Koordination mit einem möglichen Failover auf Ebene des Storage-Array. 4. Availability Groups (Verfügbarkeitsgruppen) - Vier, oder doch nur Zwei? Ein primäres Replikat erlaubt bis zu vier sekundäre Replikate innerhalb einer Verfügbarkeitsgruppe, jedoch nur zwei im Synchronen Commit Modus. Während dies zwar einen Vorteil gegenüber dem stringenten 1:1 Modell unter Database Mirroring darstellt, fällt der SQL Server 2012 damit immer noch weiter zurück hinter Oracle Data Guard mit bis zu 30 direkten Stanbdy Zielen - und vielen weiteren durch kaskadierende Ziele möglichen. Damit eignet sich Oracle Active Data Guard auch für die Bereitstellung einer Reader-Farm Skalierbarkeit für Internet-basierende Unternehmen. Mit AwaysOn Verfügbarkeitsgruppen ist dies nicht möglich. 5. Availability Groups (Verfügbarkeitsgruppen) - kein asynchrones Switchover  Die Technologie der Verfügbarkeitsgruppen wird auch als geeignetes Mittel für administrative Aufgaben positioniert - wie Upgrades oder Wartungsarbeiten. Man muss sich jedoch einem gravierendem Defizit bewusst sein: Im asynchronen Verfügbarkeitsmodus besteht die einzige Möglichkeit für Role Transition im Forced Failover mit Datenverlust! Um den Verlust von Daten durch geplante Wartungsarbeiten zu vermeiden, muss man den synchronen Verfügbarkeitsmodus konfigurieren, was jedoch ernstzunehmende Auswirkungen auf WAN Deployments nach sich zieht. Spinnt man diesen Gedanken zu Ende, kommt man zu dem Schluss, dass die Technologie der Verfügbarkeitsgruppen für geplante Wartungsarbeiten in einem derartigen Umfeld nicht effektiv genutzt werden kann. 6. Automatisches Failover - Nicht immer möglich Sowohl die SQL Server FCI, als auch Verfügbarkeitsgruppen unterstützen automatisches Failover. Möchte man diese jedoch kombinieren, wird das Ergebnis kein automatisches Failover sein. Denn ihr Zusammentreffen im Failover-Fall führt zu Race Conditions (Wettlaufsituationen), weshalb diese Konfiguration nicht länger das automatische Failover zu einem Replikat in einer Verfügbarkeitsgruppe erlaubt. Auch hier bestätigt sich wieder die tiefere Problematik von AlwaysOn, mit einer Zusammensetzung aus unterschiedlichen Technologien und der Abhängigkeit zu Windows. 7. Problematische RTO (Recovery Time Objective) Microsoft postioniert die SQL Server Multi-Subnet Clustering Architektur als brauchbare HA/DR Architektur. Bedenkt man jedoch die Problematik im Zusammenhang mit DNS Replikation und den möglichen langen Wartezeiten auf Client-Seite von bis zu 16 Minuten, sind strenge RTO Anforderungen (Recovery Time Objectives) nicht erfüllbar. Im Gegensatz zu Oracle besitzt der SQL Server keine Datenbank-integrierten Technologien, wie Oracle Fast Application Notification (FAN) oder Oracle Fast Connection Failover (FCF). 8. Problematische RPO (Recovery Point Objective) SQL Server ermöglicht Forced Failover (erzwungenes Failover), bietet jedoch keine Möglichkeit zur automatischen Übertragung der letzten Datenbits von einem alten zu einem neuen primären Replikat, wenn der Verfügbarkeitsmodus asynchron war. Oracle Data Guard hingegen bietet diese Unterstützung durch das Flush Redo Feature. Dies sichert "Zero Data Loss" und beste RPO auch in erzwungenen Failover-Situationen. 9. Lesbare Sekundäre Replikate mit Einschränkungen Aufgrund des Snapshot Isolation Transaction Level für lesbare sekundäre Replikate, besitzen diese Einschränkungen mit Auswirkung auf die primäre Datenbank. Die Bereinigung von Ghost Records auf der primären Datenbank, wird beeinflusst von lang laufenden Abfragen auf der lesabaren sekundären Datenbank. Die lesbare sekundäre Datenbank kann nicht in die Verfügbarkeitsgruppe aufgenommen werden, wenn es aktive Transaktionen auf der primären Datenbank gibt. Zusätzlich können DLL Änderungen auf der primären Datenbank durch Abfragen auf der sekundären blockiert werden. Und imkrementelle Backups werden hier nicht unterstützt.   Keine dieser Restriktionen existiert unter Oracle Data Guard.

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• Cannot login to Ubuntu 14.04 returns to the login screen

  - by Safder

  I updated to 14.04 from 12.04.03. I was using cinammon at that time. When I upgraded to 14.04 ,I got a serious problem. I was unable to login, as whenever I hit enter after entering password, it is taking me straight to login screen again.I unable to login like Guest even. So, here is my .xsession-errors file. possibly anyone could help. Thanks in advance. Script for ibus started at run_im. Script for auto started at run_im. Script for default started at run_im. init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd main process ended, respawning init: at-spi2-registryd respawning too fast, stopped init: gnome-settings-daemon main process (14717) killed by TRAP signal init: gnome-settings-daemon main process ended, respawning init: update-notifier-crash (/var/crash/_usr_bin_gnome-session.1000.crash) main process (14607) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_ibus_ibus-x11.1000.crash) main process (14623) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_x86_64-linux-gnu_bamf_bamfdaemon.1000.crash) main process (14663) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_ibus_ibus-ui-gtk3.1000.crash) main process (14620) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_gnome-session_gnome-session-check-accelerated.1000.crash) main process (14612) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_gnome-settings-daemon_gnome-settings-daemon.1000.crash) main process (14616) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_unity_unity-panel-service.1000.crash) main process (14629) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_unity-settings-daemon_unity-settings-daemon.1000.crash) main process (14625) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_update-notifier_system-crash-notification.1000.crash) main process (14662) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_gnome-session_gnome-session-check-accelerated.127.crash) main process (14613) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_share_apport_apport-gtk.1000.crash) main process (14665) terminated with status 133 init: update-notifier-crash (/var/crash/linux-image-3.13.0-24-generic.0.crash) main process (14606) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_bin_Xorg.0.crash) main process (14609) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_ibus_ibus-x11.127.crash) main process (14624) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_ibus_ibus-ui-gtk3.127.crash) main process (14622) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_gnome-settings-daemon_gnome-settings-daemon.127.crash) main process (14618) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_unity-settings-daemon_unity-settings-daemon.127.crash) main process (14628) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_x86_64-linux-gnu_bamf_bamfdaemon.127.crash) main process (14664) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_bin_gnome-session.127.crash) main process (14608) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_lib_unity_unity-panel-service.127.crash) main process (14634) terminated with status 133 init: update-notifier-crash (/var/crash/_usr_share_apport_apport-gtk.127.crash) main process (14667) terminated with status 133 init: gnome-settings-daemon main process (14843) killed by TRAP signal init: gnome-settings-daemon main process ended, respawning init: gnome-settings-daemon main process (14850) killed by TRAP signal init: gnome-settings-daemon main process ended, respawning init: gnome-session (GNOME) main process (14727) killed by TRAP signal init: gnome-settings-daemon main process (14859) killed by TRAP signal init: logrotate main process (14570) killed by TERM signal init: upstart-dbus-session-bridge main process (14683) terminated with status 1 init: Disconnected from notified D-Bus bus

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• Integrating HTML into Silverlight Applications

  - by dwahlin

  Looking for a way to display HTML content within a Silverlight application? If you haven’t tried doing that before it can be challenging at first until you know a few tricks of the trade.  Being able to display HTML is especially handy when you’re required to display RSS feeds (with embedded HTML), SQL Server Reporting Services reports, PDF files (not actually HTML – but the techniques discussed will work), or other HTML content.  In this post I'll discuss three options for displaying HTML content in Silverlight applications and describe how my company is using these techniques in client applications. Displaying HTML Overlays If you need to display HTML over a Silverlight application (such as an RSS feed containing HTML data in it) you’ll need to set the Silverlight control’s windowless parameter to true. This can be done using the object tag as shown next: <object data="data:application/x-silverlight-2," type="application/x-silverlight-2" width="100%" height="100%"> <param name="source" value="ClientBin/HTMLAndSilverlight.xap"/> <param name="onError" value="onSilverlightError" /> <param name="background" value="white" /> <param name="minRuntimeVersion" value="4.0.50401.0" /> <param name="autoUpgrade" value="true" /> <param name="windowless" value="true" /> <a href="http://go.microsoft.com/fwlink/?LinkID=149156&v=4.0.50401.0" style="text-decoration:none"> <img src="http://go.microsoft.com/fwlink/?LinkId=161376" alt="Get Microsoft Silverlight" style="border-style:none"/> </a> </object> By setting the control to “windowless” you can overlay HTML objects by using absolute positioning and other CSS techniques. Keep in mind that on Windows machines the windowless setting can result in a performance hit when complex animations or HD video are running since the plug-in content is displayed directly by the browser window. It goes without saying that you should only set windowless to true when you really need the functionality it offers. For example, if I want to display my blog’s RSS content on top of a Silverlight application I could set windowless to true and create a user control that grabbed the content and output it using a DataList control: <style type="text/css"> a {text-decoration:none;font-weight:bold;font-size:14pt;} </style> <div style="margin-top:10px; margin-left:10px;margin-right:5px;"> <asp:DataList ID="RSSDataList" runat="server" DataSourceID="RSSDataSource"> <ItemTemplate> <a href='<%# XPath("link") %>'><%# XPath("title") %></a> <br /> <%# XPath("description") %> <br /> </ItemTemplate> </asp:DataList> <asp:XmlDataSource ID="RSSDataSource" DataFile="http://weblogs.asp.net/dwahlin/rss.aspx" XPath="rss/channel/item" CacheDuration="60" runat="server" /> </div> The user control can then be placed in the page hosting the Silverlight control as shown below. This example adds a Close button, additional content to display in the overlay window and the HTML generated from the user control. <div id="RSSDiv"> <div style="background-color:#484848;border:1px solid black;height:35px;width:100%;"> <img alt="Close Button" align="right" src="Images/Close.png" onclick="HideOverlay();" style="cursor:pointer;" /> </div> <div style="overflow:auto;width:800px;height:565px;"> <div style="float:left;width:100px;height:103px;margin-left:10px;margin-top:5px;"> <img src="http://weblogs.asp.net/blogs/dwahlin/dan2008.jpg" style="border:1px solid Gray" /> </div> <div style="float:left;width:300px;height:103px;margin-top:5px;"> <a href="http://weblogs.asp.net/dwahlin" style="margin-left:10px;font-size:20pt;">Dan Wahlin's Blog</a> </div> <br /><br /><br /> <div style="clear:both;margin-top:20px;"> <uc:BlogRoller ID="BlogRoller" runat="server" /> </div> </div> </div> Of course, we wouldn’t want the RSS HTML content to be shown until requested. Once it’s requested the absolute position of where it should show above the Silverlight control can be set using standard CSS styles. The following ID selector named #RSSDiv handles hiding the overlay div shown above and determines where it will be display on the screen. #RSSDiv { background-color:White; position:absolute; top:100px; left:300px; width:800px; height:600px; border:1px solid black; display:none; } Now that the HTML content to display above the Silverlight control is set, how can we show it as a user clicks a HyperlinkButton or other control in the application? Fortunately, Silverlight provides an excellent HTML bridge that allows direct access to content hosted within a page. The following code shows two JavaScript functions that can be called from Siverlight to handle showing or hiding HTML overlay content. The two functions rely on jQuery (http://www.jQuery.com) to make it easy to select HTML objects and manipulate their properties: function ShowOverlay() { rssDiv.css('display', 'block'); } function HideOverlay() { rssDiv.css('display', 'none'); } Calling the ShowOverlay function is as simple as adding the following code into the Silverlight application within a button’s Click event handler: private void OverlayHyperlinkButton_Click(object sender, RoutedEventArgs e) { HtmlPage.Window.Invoke("ShowOverlay"); } The result of setting the Silverlight control’s windowless parameter to true and showing the HTML overlay content is shown in the following screenshot:   Thinking Outside the Box to Show HTML Content Setting the windowless parameter to true may not be a viable option for some Silverlight applications or you may simply want to go about showing HTML content a different way. The next technique I’ll show takes advantage of simple HTML, CSS and JavaScript code to handle showing HTML content while a Silverlight application is running in the browser. Keep in mind that with Silverlight’s HTML bridge feature you can always pop-up HTML content in a new browser window using code similar to the following: System.Windows.Browser.HtmlPage.Window.Navigate( new Uri("http://silverlight.net"), "_blank"); For this example I’ll demonstrate how to hide the Silverlight application while maximizing a container div containing the HTML content to show. This allows HTML content to take up the full screen area of the browser without having to set windowless to true and when done right can make the user feel like they never left the Silverlight application. The following HTML shows several div elements that are used to display HTML within the same browser window as the Silverlight application: <div id="JobPlanDiv"> <div style="vertical-align:middle"> <img alt="Close Button" align="right" src="Images/Close.png" onclick="HideJobPlanIFrame();" style="cursor:pointer;" /> </div> <div id="JobPlan_IFrame_Container" style="height:95%;width:100%;margin-top:37px;"></div> </div> The JobPlanDiv element acts as a container for two other divs that handle showing a close button and hosting an iframe that will be added dynamically at runtime. JobPlanDiv isn’t visible when the Silverlight application loads due to the following ID selector added into the page: #JobPlanDiv { position:absolute; background-color:#484848; overflow:hidden; left:0; top:0; height:100%; width:100%; display:none; } When the HTML content needs to be shown or hidden the JavaScript functions shown next can be used: var jobPlanIFrameID = 'JobPlan_IFrame'; var slHost = null; var jobPlanContainer = null; var jobPlanIFrameContainer = null; var rssDiv = null; $(document).ready(function () { slHost = $('#silverlightControlHost'); jobPlanContainer = $('#JobPlanDiv'); jobPlanIFrameContainer = $('#JobPlan_IFrame_Container'); rssDiv = $('#RSSDiv'); }); function ShowJobPlanIFrame(url) { jobPlanContainer.css('display', 'block'); $('<iframe id="' + jobPlanIFrameID + '" src="' + url + '" style="height:100%;width:100%;" />') .appendTo(jobPlanIFrameContainer); slHost.css('width', '0%'); } function HideJobPlanIFrame() { jobPlanContainer.css('display', 'none'); $('#' + jobPlanIFrameID).remove(); slHost.css('width', '100%'); } ShowJobPlanIFrame() handles showing the JobPlanDiv div and adding an iframe into it dynamically. Once JobPlanDiv is shown, the Silverlight control host has its width set to a value of 0% to allow the control to stay alive while making it invisible to the user. I found that this technique works better across multiple browsers as opposed to manipulating the Silverlight control host div’s display or visibility properties. Now that you’ve seen the code to handle showing and hiding the HTML content area, let’s switch focus to the Silverlight application. As a user clicks on a link such as “View Report” the ShowJobPlanIFrame() JavaScript function needs to be called. The following code handles that task: private void ReportHyperlinkButton_Click(object sender, RoutedEventArgs e) { ShowBrowser(_BaseUrl + "/Report.aspx"); } public void ShowBrowser(string url) { HtmlPage.Window.Invoke("ShowJobPlanIFrame", url); } Any URL can be passed into the ShowBrowser() method which handles invoking the JavaScript function. This includes standard web pages or even PDF files. We’ve used this technique frequently with our SmartPrint control (http://www.smartwebcontrols.com) which converts Silverlight screens into PDF documents and displays them. Here’s an example of the content generated:   Silverlight 4’s WebBrowser Control Both techniques shown to this point work well when Silverlight is running in-browser but not so well when it’s running out-of-browser since there’s no host page that you can access using the HTML bridge. Fortunately, Silverlight 4 provides a WebBrowser control that can be used to perform the same functionality quite easily. We’re currently using it in client applications to display PDF documents, SSRS reports and standard HTML content. Using the WebBrowser control simplifies the application quite a bit since no JavaScript is required if the application only runs out-of-browser. Here’s a simple example of defining the WebBrowser control in XAML. I typically define it in MainPage.xaml when a Silverlight Navigation template is used to create the project so that I can re-use the functionality across multiple screens. <Grid x:Name="WebBrowserGrid" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Visibility="Collapsed"> <StackPanel HorizontalAlignment="Stretch" VerticalAlignment="Stretch"> <Border Background="#484848" HorizontalAlignment="Stretch" Height="40"> <Image x:Name="WebBrowserImage" Width="100" Height="33" Cursor="Hand" HorizontalAlignment="Right" Source="/HTMLAndSilverlight;component/Assets/Images/Close.png" MouseLeftButtonDown="WebBrowserImage_MouseLeftButtonDown" /> </Border> <WebBrowser x:Name="JobPlanReportWebBrowser" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" /> </StackPanel> </Grid> Looking through the XAML you can see that a close image is defined along with the WebBrowser control. Because the URL that the WebBrowser should navigate to isn’t known at design time no value is assigned to the control’s Source property. If the XAML shown above is left “as is” you’ll find that any HTML content assigned to the WebBrowser doesn’t display properly. This is due to no height or width being set on the control. To handle this issue the following code is added into the XAML’s code-behind file to dynamically determine the height and width of the page and assign it to the WebBrowser. This is done by handling the SizeChanged event. void MainPage_SizeChanged(object sender, SizeChangedEventArgs e) { WebBrowserGrid.Height = JobPlanReportWebBrowser.Height = ActualHeight; WebBrowserGrid.Width = JobPlanReportWebBrowser.Width = ActualWidth; } When the user wants to view HTML content they click a button which executes the code shown in next: public void ShowBrowser(string url) { if (Application.Current.IsRunningOutOfBrowser) { JobPlanReportWebBrowser.NavigateToString("<html><body><iframe src='" + url + "' style='width:100%;height:97%;' /></body></html>"); WebBrowserGrid.Visibility = Visibility.Visible; } else { HtmlPage.Window.Invoke("ShowJobPlanIFrame", url); } } private void WebBrowserImage_MouseLeftButtonDown(object sender, MouseButtonEventArgs e) { WebBrowserGrid.Visibility = Visibility.Collapsed; }   Looking through the code you’ll see that it checks to see if the Silverlight application is running out-of-browser and then either displays the WebBrowser control or runs the JavaScript function discussed earlier. Although the WebBrowser control’s Source property could be assigned the URI of the page to navigate to, by assigning HTML content using the NavigateToString() method and adding an iframe, content can be shown from any site including cross-domain sites. This is especially handy when you need to grab a page from a reporting site that’s in a different domain than the Silverlight application. Here’s an example of viewing  PDF file inside of an out-of-browser application. The first image shows the application running out-of-browser before the user clicks a PDF HyperlinkButton.  The second image shows the PDF being displayed.   While there are certainly other techniques that can be used, the ones shown here have worked well for us in different applications and provide the ability to display HTML content in-browser or out-of-browser. Feel free to add a comment if you have another tip or trick you like to use when working with HTML content in Silverlight applications.   Download Code Sample   For more information about onsite, online and video training, mentoring and consulting solutions for .NET, SharePoint or Silverlight please visit http://www.thewahlingroup.com.

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• OAM OVD integration - Error Encounterd while performance test "LDAP response read timed out, timeout used:2000ms"

  - by siddhartha_sinha

  While working on OAM OVD integration for one of my client, I have been involved in the performance test of the products wherein I encountered OAM authentication failures while talking to OVD during heavy load. OAM logs revealed the following: oracle.security.am.common.policy.common.response.ResponseException: oracle.security.am.engines.common.identity.provider.exceptions.IdentityProviderException: OAMSSA-20012: Exception in getting user attributes for user : dummy_user1, idstore MyIdentityStore with exception javax.naming.NamingException: LDAP response read timed out, timeout used:2000ms.; remaining name 'ou=people,dc=oracle,dc=com' at oracle.security.am.common.policy.common.response.IdentityValueProvider.getUserAttribute(IdentityValueProvider.java:271) ... During the authentication and authorization process, OAM complains that the LDAP repository is taking too long to return user attributes.The default value is 2 seconds as can be seen from the exception, "2000ms". While troubleshooting the issue, it was found that we can increase the ldap read timeout in oam-config.xml.  For reference, the attribute to add in the oam-config.xml file is: <Setting Name="LdapReadTimeout" Type="xsd:string">2000</Setting> However it is not recommended to increase the time out unless it is absolutely necessary and ensure that back-end directory servers are working fine. Rather I took the path of tuning OVD in the following manner: 1) Navigate to ORACLE_INSTANCE/config/OPMN/opmn folder and edit opmn.xml. Search for <data id="java-options" ………> and edit the contents of the file with the highlighted items: <category id="start-options"><data id="java-bin" value="$ORACLE_HOME/jdk/bin/java"/><data id="java-options" value="-server -Xms1024m -Xmx1024m -Dvde.soTimeoutBackend=0 -Didm.oracle.home=$ORACLE_HOME -Dcommon.components.home=$ORACLE_HOME/../oracle_common -XX:+PrintGCDetails -XX:+PrintGCDateStamps -Xloggc:/opt/bea/Middleware/asinst_1/diagnostics/logs/OVD/ovd1/ovdGClog.log -XX:+UseConcMarkSweepGC -Doracle.security.jps.config=$ORACLE_INSTANCE/config/JPS/jps-config-jse.xml"/><data id="java-classpath" value="$ORACLE_HOME/ovd/jlib/vde.jar$:$ORACLE_HOME/jdbc/lib/ojdbc6.jar"/></category></module-data><stop timeout="120"/><ping interval="60"/></process-type> When the system is busy, a ping from the Oracle Process Manager and Notification Server (OPMN) to Oracle Virtual Directory may fail. As a result, OPMN will restart Oracle Virtual Directory after 20 seconds (the default ping interval). To avoid this, consider increasing the ping interval to 60 seconds or more. 2) Navigate to ORACLE_INSTANCE/config/OVD/ovd1 folder.Open listeners.os_xml file and perform the following changes: · Search for <ldap id=”Ldap Endpoint”…….> and point the cursor to that line. · Change threads count to 200. · Change anonymous bind to Deny. · Change workQueueCapacity to 8096. Add a new parameter <useNIO> and set its value to false viz: <useNIO>false</useNio> Snippet: <ldap version="8" id="LDAP Endpoint"> ....... .......  <socketOptions><backlog>128</backlog>         <reuseAddress>false</reuseAddress>         <keepAlive>false</keepAlive>         <tcpNoDelay>true</tcpNoDelay>         <readTimeout>0</readTimeout>      </socketOptions> <useNIO>false</useNIO></ldap> Restart OVD server. For more information on OVD tuneup refer to http://docs.oracle.com/cd/E25054_01/core.1111/e10108/ovd.htm. Please Note: There were few patches released from OAM side for performance tune-up as well. Will provide the updates shortly !!!

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• Hierarchical View/ViewModel/Presenters in MVPVM

  - by Brian Flynn

  I've been working with MVVM for a while, but I've recently started using MVPVM and I want to know how to create hierarchial View/ViewModel/Presenter app using this pattern. In MVVM I would typically build my application using a hierarchy of Views and corresponding ViewModels e.g. I might define 3 views as follows: The View Models for these views would be as follows: public class AViewModel { public string Text { get { return "This is A!"; } } public object Child1 { get; set; } public object Child2 { get; set; } } public class BViewModel { public string Text { get { return "This is B!"; } } } public class CViewModel { public string Text { get { return "This is C!"; } } } In would then have some data templates to say that BViewModel and CViewModel should be presented using View B and View C: <DataTemplate DataType="{StaticResource local:BViewModel}"> <local:BView/> </DataTemplate> <DataTemplate DataType="{StaticResource local:CViewModel}"> <local:CView/> </DataTemplate> The final step would be to put some code in AViewModel that would assign values to Child1 and Child2: public AViewModel() { this.Child1 = new AViewModel(); this.Child2 = new BViewModel(); } The result of all this would be a screen that looks something like: Doing this in MVPVM would be fairly simple - simply moving the code in AViewModel's constructor to APresenter: public class APresenter { .... public void WireUp() { ViewModel.Child1 = new BViewModel(); ViewModel.Child2 = new CViewModel(); } } But If I want to have business logic for BViewModel and CViewModel I would need to have a BPresenter and a CPresenter - the problem is, Im not sure where the best place to put these are. I could store references to the presenter for AViewModel.Child1 and AViewModel.Child2 in APresenter i.e.: public class APresenter : IPresenter { private IPresenter child1Presenter; private IPresenter child2Presenter; public void WireUp() { child1Presenter = new BPresenter(); child1Presenter.WireUp(); child2Presenter = new CPresenter(); child2Presenter.WireUp(); ViewModel.Child1 = child1Presenter.ViewModel; ViewModel.Child2 = child2Presenter.ViewModel; } } But this solution seems inelegant compared to the MVVM approach. I have to keep track of both the presenter and the view model and ensure they stay in sync. If, for example, I wanted a button on View A, which, when clicked swapped the View's in Child1 and Child2, I might have a command that did the following: var temp = ViewModel.Child1; ViewModel.Child1 = ViewModel.Child2; ViewModel.Child2 = temp; This would work as far as swapping the view's on screen (assuming the correct Property Change notification code is in place), but now my APresenter.child1Presenter is pointing to the presenter for AViewModel.Child2, and APresenter.child2Presenter is pointing to the presenter for AViewModel.Child1. If something accesses APresenter.child1Presenter, any changes will actually happen to AViewModel.Child2. I can imagine this leading to all sorts of debugging fun. I know that I may be misunderstanding the pattern, and if this is the case a clarification of what Im doing wrong would be appreciated.

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• PowerShell Script to Create PowerShell Profile

  - by Brian Jackett

  Utilizing a PowerShell profile can help any PowerShell user save time getting up and running with their work.  For those unfamiliar a PowerShell profile is a file you can store any PowerShell commands that you want to run when you fire up a PowerShell console (or ISE.)  In my typical profiles (example here) I load assemblies (like SharePoint 2007 DLL), set aliases, set environment variable values (such as max history), and perform other general customizations to make my work easier.  Below is a sample script that will check to see if a PowerShell profile (Console or ISE) exists and create it if not found.  The .ps1 script file version can also be downloaded from my SkyDrive here. Note: if downloading the .ps1 file, be sure you have enabled unsigned scripts to run on your machine as I have not signed mine.   $folderExists = test-path -path $Env:UserProfile\Documents\WindowsPowerShell if($folderExists -eq $false) { new-item -type directory -path $Env:UserProfile\Documents\WindowsPowerShell > $null echo "Containing folder for profile created at: $Env:UserProfile\Documents\WindowsPowerShell" }   $profileExists = test-path -path $profile if($profileExists -eq $false) { new-item -type file -path $profile > $null echo "Profile file created at: $profile" }     A few things to note while going through the above script. $Env:UserProfile represents the personal user folder (c:\documents and settings…. on older OSes like XP and c:\Users… on Win 7) so it adapts to whichever OS you are running but was tested against Windows 7 and Windows Server 2008 R2. “ > $null” sends the command to a null stream.  Essentially this is equivalent to DOS scripting of “@ECHO OFF” by suppressing echoing the command just run, but only for the specific command it is appended to.  I haven’t yet found a better way to accomplish command suppression, but this is definitely not required for the script to work. $profile represent a standard variable to the file path of the profile file.  It is dynamic based on whether you are running PowerShell Console or ISE.   Conclusion     In less than two weeks (Apr. 10th to be exact) I’ll be heading down to SharePoint Saturday Charlotte (SPSCLT) to give two presentations on using PowerShell with SharePoint.  Since I’ll be prepping a lot of material for PowerShell I thought it only appropriate to pass along this nice little script I recently created.  If you’ve never used a PowerShell profile this is a great chance to start using one.  If you’ve been using a profile before, perhaps you learned a trick or two to add to your toolbox.  For those of you in the Charlotte, NC area sign up for the SharePoint Saturday and see some great content and community with great folks.         -Frog Out

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• Skip “Next Links” with the PageZipper Bookmarklet

  - by Asian Angel

  No matter what browser you use sooner or later you will run across a website with an endless number of “next links” used for the sole purpose of generating page views. Now you can simply scroll through those articles without the “next links” using the PageZipper Bookmarklet. The Problem Here is a perfect example of a page view generating article. As you can see our browser is in a non-maximized state and the first part of the article takes up very little room in the browser window. Absolutely horrible… The PageZipper Bookmarklet in Action The bookmarklet is very easy to set up in your browser…simply drag it to your “Bookmarks Toolbar” and you are ready to go. Switching tabs back to the article we never even needed to refresh the page. One nice little click on our new bookmarklet and… It immediately went to work. When you use PageZipper you will see a page count in the upper right corner of the browser window area as shown here. You can see the transition between pages here…nice and smooth. When using the bookmarklet just keep scrolling down as needed to read the entire article. Six pages of reading condensed into one without having to click a single link. Now that is nice! Conclusion If you despise those irritating “next links” then the PageZipper Bookmarklet will be a perfect addition to your favorite browser. Links Add the PageZipper Bookmarklet to Your Favorite Browser Similar Articles Productive Geek Tips Merge a Series of Web Pages into One with PageZipperSee Where Shortened URLs “Link To” in Your Favorite BrowserBookmarklet Fun: Check Google Analytics for Today [update]Add a Google Translation Bar to Your Favorite BrowserShare Your Favorite Webpages with the AddThis Bookmarklet TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips Revo Uninstaller Pro Registry Mechanic 9 for Windows PC Tools Internet Security Suite 2010 PCmover Professional Beware Hover Kitties Test Drive Mobile Phones Online With TryPhone Ben & Jerry’s Free Cone Day, 3/23/10 New Stinger from McAfee Helps Remove ‘FakeAlert’ Threats Google Apps Marketplace: Tools & Services For Google Apps Users Get News Quick and Precise With Newser

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• ARM TechCon 2013: Oracle, ARM expand collaboration on servers, Internet of Things

  - by Henrik Stahl

  If you have been following Java news, you are already aware of the fact that there has been a lot of investment in Java for ARM-based devices and servers over the last couple of years (news, more news, even more, and lots more). We have released Java ME Embedded binaries for ARM Cortex-M micro controllers, Java SE Embedded for ARM application processors, and a port of the Oracle JDK for ARM-based servers. We have been making Java available to the Beagleboard, Raspberry Pi and Lego Mindstorms/LeJOS communities and worked with them and the Java User Groups to evangelize Java as a great development environment for IoT devices. We have announced commercial relationships with Freescale, Qualcomm, Gemalto M2M, SIMCom to name a few. ARM and Freescale on their side have joined the JCP, recently been voted in as members of the Executive Committee, and have worked with Oracle to evangelize Java in their ecosystem. It is with this background, Nandini Ramani, Vice President, Java Platform at Oracle, announced a expanded collaboration with ARM in a TechCon 2013 keynote titled "Enabling Compelling Services for IoT". To summarize the announcement: ARM and Oracle will work together on interoperability between the ARM Sensinode communications stack (based on CoAP, DTLS and 6LoWPAN) and Oracle's Java ME, Java SE and middleware products. ARM will donate the Sensinode CoAP protocol engine to OpenJDK to stimulate broad adoption of the CoAP protocol, and work with Oracle to extend the relevant Java specifications with CoAP support. CoAP (Constrained Application Protocol) is an IETF specification that provides a low-bandwidth request/response protocol suitable for IoT applications. ARM will work with Oracle and Freescale to enable the mbed Hardware Abstraction Layer (HAL) to act as a portability layer for Java ME Embedded. Oracle will enable mbed as a tier one platform for Java ME Embedded. Over time, this effort will allow any mbed-enabled platforms (mostly based on Cortex-M microcontrollers) to work with off the shelf Java ME Embedded binaries, extending the reach of Java ME into IoT edge nodes. In Nandini's keynote, Oracle showed a roadmap to port the Oracle JDK for Linux on 64-bit ARMv8 servers in the 2015 time frame, preceded by an extended early access program. We expect this binary to have full feature parity with Oracle JDK on other platforms, and be available under the same royalty-free license. This effort has been going on for some time, but is now accelerated due to availability of hardware from Applied Micro. Oracle will be working with Applied Micro on the ARMv8 port, and on optimizing Java for their X-Gene products. Oracle and ARM will work closely on IoT architecture, and on evangelizing Java on ARM for both servers and IoT devices. These announcements reinforce Java's position as a first-class citizen in the ARM ecosystem, and signal a commitment from us to collaborate on driving standards and open ecosystem for the Internet of Things. If you are active in this area and not already in touch with us, or interested in learning more - please reach out to us!

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• A Taxonomy of Numerical Methods v1

  - by JoshReuben

  Numerical Analysis – When, What, (but not how) Once you understand the Math & know C++, Numerical Methods are basically blocks of iterative & conditional math code. I found the real trick was seeing the forest for the trees – knowing which method to use for which situation. Its pretty easy to get lost in the details – so I’ve tried to organize these methods in a way that I can quickly look this up. I’ve included links to detailed explanations and to C++ code examples. I’ve tried to classify Numerical methods in the following broad categories: Solving Systems of Linear Equations Solving Non-Linear Equations Iteratively Interpolation Curve Fitting Optimization Numerical Differentiation & Integration Solving ODEs Boundary Problems Solving EigenValue problems Enjoy – I did ! Solving Systems of Linear Equations Overview Solve sets of algebraic equations with x unknowns The set is commonly in matrix form Gauss-Jordan Elimination http://en.wikipedia.org/wiki/Gauss%E2%80%93Jordan_elimination C++: http://www.codekeep.net/snippets/623f1923-e03c-4636-8c92-c9dc7aa0d3c0.aspx Produces solution of the equations & the coefficient matrix Efficient, stable 2 steps: · Forward Elimination – matrix decomposition: reduce set to triangular form (0s below the diagonal) or row echelon form. If degenerate, then there is no solution · Backward Elimination –write the original matrix as the product of ints inverse matrix & its reduced row-echelon matrix à reduce set to row canonical form & use back-substitution to find the solution to the set Elementary ops for matrix decomposition: · Row multiplication · Row switching · Add multiples of rows to other rows Use pivoting to ensure rows are ordered for achieving triangular form LU Decomposition http://en.wikipedia.org/wiki/LU_decomposition C++: http://ganeshtiwaridotcomdotnp.blogspot.co.il/2009/12/c-c-code-lu-decomposition-for-solving.html Represent the matrix as a product of lower & upper triangular matrices A modified version of GJ Elimination Advantage – can easily apply forward & backward elimination to solve triangular matrices Techniques: · Doolittle Method – sets the L matrix diagonal to unity · Crout Method - sets the U matrix diagonal to unity Note: both the L & U matrices share the same unity diagonal & can be stored compactly in the same matrix Gauss-Seidel Iteration http://en.wikipedia.org/wiki/Gauss%E2%80%93Seidel_method C++: http://www.nr.com/forum/showthread.php?t=722 Transform the linear set of equations into a single equation & then use numerical integration (as integration formulas have Sums, it is implemented iteratively). an optimization of Gauss-Jacobi: 1.5 times faster, requires 0.25 iterations to achieve the same tolerance Solving Non-Linear Equations Iteratively find roots of polynomials – there may be 0, 1 or n solutions for an n order polynomial use iterative techniques Iterative methods · used when there are no known analytical techniques · Requires set functions to be continuous & differentiable · Requires an initial seed value – choice is critical to convergence à conduct multiple runs with different starting points & then select best result · Systematic - iterate until diminishing returns, tolerance or max iteration conditions are met · bracketing techniques will always yield convergent solutions, non-bracketing methods may fail to converge Incremental method if a nonlinear function has opposite signs at 2 ends of a small interval x1 & x2, then there is likely to be a solution in their interval – solutions are detected by evaluating a function over interval steps, for a change in sign, adjusting the step size dynamically. Limitations – can miss closely spaced solutions in large intervals, cannot detect degenerate (coinciding) solutions, limited to functions that cross the x-axis, gives false positives for singularities Fixed point method http://en.wikipedia.org/wiki/Fixed-point_iteration C++: http://books.google.co.il/books?id=weYj75E_t6MC&pg=PA79&lpg=PA79&dq=fixed+point+method++c%2B%2B&source=bl&ots=LQ-5P_taoC&sig=lENUUIYBK53tZtTwNfHLy5PEWDk&hl=en&sa=X&ei=wezDUPW1J5DptQaMsIHQCw&redir_esc=y#v=onepage&q=fixed%20point%20method%20%20c%2B%2B&f=false Algebraically rearrange a solution to isolate a variable then apply incremental method Bisection method http://en.wikipedia.org/wiki/Bisection_method C++: http://numericalcomputing.wordpress.com/category/algorithms/ Bracketed - Select an initial interval, keep bisecting it ad midpoint into sub-intervals and then apply incremental method on smaller & smaller intervals – zoom in Adv: unaffected by function gradient à reliable Disadv: slow convergence False Position Method http://en.wikipedia.org/wiki/False_position_method C++: http://www.dreamincode.net/forums/topic/126100-bisection-and-false-position-methods/ Bracketed - Select an initial interval , & use the relative value of function at interval end points to select next sub-intervals (estimate how far between the end points the solution might be & subdivide based on this) Newton-Raphson method http://en.wikipedia.org/wiki/Newton's_method C++: http://www-users.cselabs.umn.edu/classes/Summer-2012/csci1113/index.php?page=./newt3 Also known as Newton's method Convenient, efficient Not bracketed – only a single initial guess is required to start iteration – requires an analytical expression for the first derivative of the function as input. Evaluates the function & its derivative at each step. Can be extended to the Newton MutiRoot method for solving multiple roots Can be easily applied to an of n-coupled set of non-linear equations – conduct a Taylor Series expansion of a function, dropping terms of order n, rewrite as a Jacobian matrix of PDs & convert to simultaneous linear equations !!! Secant Method http://en.wikipedia.org/wiki/Secant_method C++: http://forum.vcoderz.com/showthread.php?p=205230 Unlike N-R, can estimate first derivative from an initial interval (does not require root to be bracketed) instead of inputting it Since derivative is approximated, may converge slower. Is fast in practice as it does not have to evaluate the derivative at each step. Similar implementation to False Positive method Birge-Vieta Method http://mat.iitm.ac.in/home/sryedida/public_html/caimna/transcendental/polynomial%20methods/bv%20method.html C++: http://books.google.co.il/books?id=cL1boM2uyQwC&pg=SA3-PA51&lpg=SA3-PA51&dq=Birge-Vieta+Method+c%2B%2B&source=bl&ots=QZmnDTK3rC&sig=BPNcHHbpR_DKVoZXrLi4nVXD-gg&hl=en&sa=X&ei=R-_DUK2iNIjzsgbE5ID4Dg&redir_esc=y#v=onepage&q=Birge-Vieta%20Method%20c%2B%2B&f=false combines Horner's method of polynomial evaluation (transforming into lesser degree polynomials that are more computationally efficient to process) with Newton-Raphson to provide a computational speed-up Interpolation Overview Construct new data points for as close as possible fit within range of a discrete set of known points (that were obtained via sampling, experimentation) Use Taylor Series Expansion of a function f(x) around a specific value for x Linear Interpolation http://en.wikipedia.org/wiki/Linear_interpolation C++: http://www.hamaluik.com/?p=289 Straight line between 2 points à concatenate interpolants between each pair of data points Bilinear Interpolation http://en.wikipedia.org/wiki/Bilinear_interpolation C++: http://supercomputingblog.com/graphics/coding-bilinear-interpolation/2/ Extension of the linear function for interpolating functions of 2 variables – perform linear interpolation first in 1 direction, then in another. Used in image processing – e.g. texture mapping filter. Uses 4 vertices to interpolate a value within a unit cell. Lagrange Interpolation http://en.wikipedia.org/wiki/Lagrange_polynomial C++: http://www.codecogs.com/code/maths/approximation/interpolation/lagrange.php For polynomials Requires recomputation for all terms for each distinct x value – can only be applied for small number of nodes Numerically unstable Barycentric Interpolation http://epubs.siam.org/doi/pdf/10.1137/S0036144502417715 C++: http://www.gamedev.net/topic/621445-barycentric-coordinates-c-code-check/ Rearrange the terms in the equation of the Legrange interpolation by defining weight functions that are independent of the interpolated value of x Newton Divided Difference Interpolation http://en.wikipedia.org/wiki/Newton_polynomial C++: http://jee-appy.blogspot.co.il/2011/12/newton-divided-difference-interpolation.html Hermite Divided Differences: Interpolation polynomial approximation for a given set of data points in the NR form - divided differences are used to approximately calculate the various differences. For a given set of 3 data points , fit a quadratic interpolant through the data Bracketed functions allow Newton divided differences to be calculated recursively Difference table Cubic Spline Interpolation http://en.wikipedia.org/wiki/Spline_interpolation C++: https://www.marcusbannerman.co.uk/index.php/home/latestarticles/42-articles/96-cubic-spline-class.html Spline is a piecewise polynomial Provides smoothness – for interpolations with significantly varying data Use weighted coefficients to bend the function to be smooth & its 1st & 2nd derivatives are continuous through the edge points in the interval Curve Fitting A generalization of interpolating whereby given data points may contain noise à the curve does not necessarily pass through all the points Least Squares Fit http://en.wikipedia.org/wiki/Least_squares C++: http://www.ccas.ru/mmes/educat/lab04k/02/least-squares.c Residual – difference between observed value & expected value Model function is often chosen as a linear combination of the specified functions Determines: A) The model instance in which the sum of squared residuals has the least value B) param values for which model best fits data Straight Line Fit Linear correlation between independent variable and dependent variable Linear Regression http://en.wikipedia.org/wiki/Linear_regression C++: http://www.oocities.org/david_swaim/cpp/linregc.htm Special case of statistically exact extrapolation Leverage least squares Given a basis function, the sum of the residuals is determined and the corresponding gradient equation is expressed as a set of normal linear equations in matrix form that can be solved (e.g. using LU Decomposition) Can be weighted - Drop the assumption that all errors have the same significance –-> confidence of accuracy is different for each data point. Fit the function closer to points with higher weights Polynomial Fit - use a polynomial basis function Moving Average http://en.wikipedia.org/wiki/Moving_average C++: http://www.codeproject.com/Articles/17860/A-Simple-Moving-Average-Algorithm Used for smoothing (cancel fluctuations to highlight longer-term trends & cycles), time series data analysis, signal processing filters Replace each data point with average of neighbors. Can be simple (SMA), weighted (WMA), exponential (EMA). Lags behind latest data points – extra weight can be given to more recent data points. Weights can decrease arithmetically or exponentially according to distance from point. Parameters: smoothing factor, period, weight basis Optimization Overview Given function with multiple variables, find Min (or max by minimizing –f(x)) Iterative approach Efficient, but not necessarily reliable Conditions: noisy data, constraints, non-linear models Detection via sign of first derivative - Derivative of saddle points will be 0 Local minima Bisection method Similar method for finding a root for a non-linear equation Start with an interval that contains a minimum Golden Search method http://en.wikipedia.org/wiki/Golden_section_search C++: http://www.codecogs.com/code/maths/optimization/golden.php Bisect intervals according to golden ratio 0.618.. Achieves reduction by evaluating a single function instead of 2 Newton-Raphson Method Brent method http://en.wikipedia.org/wiki/Brent's_method C++: http://people.sc.fsu.edu/~jburkardt/cpp_src/brent/brent.cpp Based on quadratic or parabolic interpolation – if the function is smooth & parabolic near to the minimum, then a parabola fitted through any 3 points should approximate the minima – fails when the 3 points are collinear , in which case the denominator is 0 Simplex Method http://en.wikipedia.org/wiki/Simplex_algorithm C++: http://www.codeguru.com/cpp/article.php/c17505/Simplex-Optimization-Algorithm-and-Implemetation-in-C-Programming.htm Find the global minima of any multi-variable function Direct search – no derivatives required At each step it maintains a non-degenerative simplex – a convex hull of n+1 vertices. Obtains the minimum for a function with n variables by evaluating the function at n-1 points, iteratively replacing the point of worst result with the point of best result, shrinking the multidimensional simplex around the best point. Point replacement involves expanding & contracting the simplex near the worst value point to determine a better replacement point Oscillation can be avoided by choosing the 2nd worst result Restart if it gets stuck Parameters: contraction & expansion factors Simulated Annealing http://en.wikipedia.org/wiki/Simulated_annealing C++: http://code.google.com/p/cppsimulatedannealing/ Analogy to heating & cooling metal to strengthen its structure Stochastic method – apply random permutation search for global minima - Avoid entrapment in local minima via hill climbing Heating schedule - Annealing schedule params: temperature, iterations at each temp, temperature delta Cooling schedule – can be linear, step-wise or exponential Differential Evolution http://en.wikipedia.org/wiki/Differential_evolution C++: http://www.amichel.com/de/doc/html/ More advanced stochastic methods analogous to biological processes: Genetic algorithms, evolution strategies Parallel direct search method against multiple discrete or continuous variables Initial population of variable vectors chosen randomly – if weighted difference vector of 2 vectors yields a lower objective function value then it replaces the comparison vector Many params: #parents, #variables, step size, crossover constant etc Convergence is slow – many more function evaluations than simulated annealing Numerical Differentiation Overview 2 approaches to finite difference methods: · A) approximate function via polynomial interpolation then differentiate · B) Taylor series approximation – additionally provides error estimate Finite Difference methods http://en.wikipedia.org/wiki/Finite_difference_method C++: http://www.wpi.edu/Pubs/ETD/Available/etd-051807-164436/unrestricted/EAMPADU.pdf Find differences between high order derivative values - Approximate differential equations by finite differences at evenly spaced data points Based on forward & backward Taylor series expansion of f(x) about x plus or minus multiples of delta h. Forward / backward difference - the sums of the series contains even derivatives and the difference of the series contains odd derivatives – coupled equations that can be solved. Provide an approximation of the derivative within a O(h^2) accuracy There is also central difference & extended central difference which has a O(h^4) accuracy Richardson Extrapolation http://en.wikipedia.org/wiki/Richardson_extrapolation C++: http://mathscoding.blogspot.co.il/2012/02/introduction-richardson-extrapolation.html A sequence acceleration method applied to finite differences Fast convergence, high accuracy O(h^4) Derivatives via Interpolation Cannot apply Finite Difference method to discrete data points at uneven intervals – so need to approximate the derivative of f(x) using the derivative of the interpolant via 3 point Lagrange Interpolation Note: the higher the order of the derivative, the lower the approximation precision Numerical Integration Estimate finite & infinite integrals of functions More accurate procedure than numerical differentiation Use when it is not possible to obtain an integral of a function analytically or when the function is not given, only the data points are Newton Cotes Methods http://en.wikipedia.org/wiki/Newton%E2%80%93Cotes_formulas C++: http://www.siafoo.net/snippet/324 For equally spaced data points Computationally easy – based on local interpolation of n rectangular strip areas that is piecewise fitted to a polynomial to get the sum total area Evaluate the integrand at n+1 evenly spaced points – approximate definite integral by Sum Weights are derived from Lagrange Basis polynomials Leverage Trapezoidal Rule for default 2nd formulas, Simpson 1/3 Rule for substituting 3 point formulas, Simpson 3/8 Rule for 4 point formulas. For 4 point formulas use Bodes Rule. Higher orders obtain more accurate results Trapezoidal Rule uses simple area, Simpsons Rule replaces the integrand f(x) with a quadratic polynomial p(x) that uses the same values as f(x) for its end points, but adds a midpoint Romberg Integration http://en.wikipedia.org/wiki/Romberg's_method C++: http://code.google.com/p/romberg-integration/downloads/detail?name=romberg.cpp&can=2&q= Combines trapezoidal rule with Richardson Extrapolation Evaluates the integrand at equally spaced points The integrand must have continuous derivatives Each R(n,m) extrapolation uses a higher order integrand polynomial replacement rule (zeroth starts with trapezoidal) à a lower triangular matrix set of equation coefficients where the bottom right term has the most accurate approximation. The process continues until the difference between 2 successive diagonal terms becomes sufficiently small. Gaussian Quadrature http://en.wikipedia.org/wiki/Gaussian_quadrature C++: http://www.alglib.net/integration/gaussianquadratures.php Data points are chosen to yield best possible accuracy – requires fewer evaluations Ability to handle singularities, functions that are difficult to evaluate The integrand can include a weighting function determined by a set of orthogonal polynomials. Points & weights are selected so that the integrand yields the exact integral if f(x) is a polynomial of degree <= 2n+1 Techniques (basically different weighting functions): · Gauss-Legendre Integration w(x)=1 · Gauss-Laguerre Integration w(x)=e^-x · Gauss-Hermite Integration w(x)=e^-x^2 · Gauss-Chebyshev Integration w(x)= 1 / Sqrt(1-x^2) Solving ODEs Use when high order differential equations cannot be solved analytically Evaluated under boundary conditions RK for systems – a high order differential equation can always be transformed into a coupled first order system of equations Euler method http://en.wikipedia.org/wiki/Euler_method C++: http://rosettacode.org/wiki/Euler_method First order Runge–Kutta method. Simple recursive method – given an initial value, calculate derivative deltas. Unstable & not very accurate (O(h) error) – not used in practice A first-order method - the local error (truncation error per step) is proportional to the square of the step size, and the global error (error at a given time) is proportional to the step size In evolving solution between data points xn & xn+1, only evaluates derivatives at beginning of interval xn à asymmetric at boundaries Higher order Runge Kutta http://en.wikipedia.org/wiki/Runge%E2%80%93Kutta_methods C++: http://www.dreamincode.net/code/snippet1441.htm 2nd & 4th order RK - Introduces parameterized midpoints for more symmetric solutions à accuracy at higher computational cost Adaptive RK – RK-Fehlberg – estimate the truncation at each integration step & automatically adjust the step size to keep error within prescribed limits. At each step 2 approximations are compared – if in disagreement to a specific accuracy, the step size is reduced Boundary Value Problems Where solution of differential equations are located at 2 different values of the independent variable x à more difficult, because cannot just start at point of initial value – there may not be enough starting conditions available at the end points to produce a unique solution An n-order equation will require n boundary conditions – need to determine the missing n-1 conditions which cause the given conditions at the other boundary to be satisfied Shooting Method http://en.wikipedia.org/wiki/Shooting_method C++: http://ganeshtiwaridotcomdotnp.blogspot.co.il/2009/12/c-c-code-shooting-method-for-solving.html Iteratively guess the missing values for one end & integrate, then inspect the discrepancy with the boundary values of the other end to adjust the estimate Given the starting boundary values u1 & u2 which contain the root u, solve u given the false position method (solving the differential equation as an initial value problem via 4th order RK), then use u to solve the differential equations. Finite Difference Method For linear & non-linear systems Higher order derivatives require more computational steps – some combinations for boundary conditions may not work though Improve the accuracy by increasing the number of mesh points Solving EigenValue Problems An eigenvalue can substitute a matrix when doing matrix multiplication à convert matrix multiplication into a polynomial EigenValue For a given set of equations in matrix form, determine what are the solution eigenvalue & eigenvectors Similar Matrices - have same eigenvalues. Use orthogonal similarity transforms to reduce a matrix to diagonal form from which eigenvalue(s) & eigenvectors can be computed iteratively Jacobi method http://en.wikipedia.org/wiki/Jacobi_method C++: http://people.sc.fsu.edu/~jburkardt/classes/acs2_2008/openmp/jacobi/jacobi.html Robust but Computationally intense – use for small matrices < 10x10 Power Iteration http://en.wikipedia.org/wiki/Power_iteration For any given real symmetric matrix, generate the largest single eigenvalue & its eigenvectors Simplest method – does not compute matrix decomposition à suitable for large, sparse matrices Inverse Iteration Variation of power iteration method – generates the smallest eigenvalue from the inverse matrix Rayleigh Method http://en.wikipedia.org/wiki/Rayleigh's_method_of_dimensional_analysis Variation of power iteration method Rayleigh Quotient Method Variation of inverse iteration method Matrix Tri-diagonalization Method Use householder algorithm to reduce an NxN symmetric matrix to a tridiagonal real symmetric matrix vua N-2 orthogonal transforms     Whats Next Outside of Numerical Methods there are lots of different types of algorithms that I’ve learned over the decades: Data Mining – (I covered this briefly in a previous post: http://geekswithblogs.net/JoshReuben/archive/2007/12/31/ssas-dm-algorithms.aspx ) Search & Sort Routing Problem Solving Logical Theorem Proving Planning Probabilistic Reasoning Machine Learning Solvers (eg MIP) Bioinformatics (Sequence Alignment, Protein Folding) Quant Finance (I read Wilmott’s books – interesting) Sooner or later, I’ll cover the above topics as well.

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• ¿Oficina sin papeles?

  - by [email protected]

  Recientemente hemos organizado un evento de Digitalización para mostrar algunos de los últimos productos de Oracle en éste área.Siempre tendemos a pensar que en España estamos retrasados en estas tecnologías y que el mercado no está preparado para eliminar el papel. En algunos casos es cierto, pero también nos hemos llevado sorpresas con clientes extremadamente avanzados en la gestión electrónica del papel.Para los clientes que no tienen una solución corporativa ya desplegada, nuestra oferta de Imaging les parece completa e integrada, porque les permite digitalizar el papel en el punto más cercano a su recepción y posteriormente realizar todo el trámite interno de forma digital.Este proceso es el que se muestra en la siguiente imágen: Sobre todo en el entorno financiero los clientes ya tienen grandes infraestructuras desplegadas (algunos con funcionalidades muy sofisticadas que han desarrollado a medida durante estos últimos años).En estos casos, su interés está centrado en 2 capacidades clave de nuestros productos: La digitalización distribuidaEl OCR inteligenteCuando ya disponemos de una infraestructura de digitalización centralizada, tenemos varios puntos de mejora con los que conseguir mayores ratios de ahorro en la gestión del papel. Uno de ellos es digitalizar en origen, de forma que ahorraremos en logística de desplazamiento y almacenamiento de papel (reducimos valijas) y en velocidad de arranque de los procesos (desde el momento de la recepción).El hecho de poder hacer esto sólo con un explorador de internet es muy novedoso para los clientes.El no instalar ninguna pieza de software de cliente parece que es un requisito que muchos clientes estaban demandando desde hace tiempo. De hecho, estamos realizando demos en vivo con un escáner del cliente (solo necesitamos el driver de windows para ese escáner). El resultado es sorprendente porque mostramos cómo: escaneamos con sólo un explorador de internet; el documento escaneado, con sus metadatos, se incorporan al gestor documental; y se dispara su workflow de aprobación.Hacer esto en segundos es algo que genera mucho interés en los clientes de cara a acelerar la gestión de muchos de sus trámites en papel.Por último, lo más novedoso de la oferta es el OCR inteligente. Hay quien ya tiene absolutamente operativas sus infraestructuras de digitalización con todas estas capacidades, y buscan un paso más allá con el reconocimiento inteligente de todos los metadatos posibles.El beneficio es rápido, claramente cuantificable y muy alto. El software de OCR inteligente se basa en lógica difusa y nos permite definir los umbrales de validación totalmente adecuados a nuestros factores de confianza. Es decir, configuramos el umbral para que cuando el software acepta un acierto tengamos la seguridad total de que dichos metadatos se han reconocido perfectamente. En caso contrario, el software lanza una validación manual.¿Qué pasa si conseguimos que para determinados documentos, el 40%, 50%, 60% o incluso el 70% u 80% de ellos fueran procesados 100% automáticamente?. El ahorro es inmenso, la reducción del tiempo de proceso también, y la integración con nuestras infraestructuras de digitalización es muy sencilla (basta con desviar unos cuantos documentos de un tipo concreto a Oracle Forms Recognition y evaluar el resultado).Os animo a que veáis estos productos y consigamos hacer realidad la reducción de papel.

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• Teamviewer 8 on Kubuntu 13.04 won't start

  - by kirokko

  The problem is I can't run Teamviewer on Kubuntu. That problem exists for me since 12.10 and I as I remember, it was with the 7th version either. I download official package from officical web site, for 64 bit system. Install it, then install all dependencies (apt-get install -f). When I start it, window with License agreement appears and I can't agree with it, because I don't see anything, even mouse cursor is invisible on window area. Here's the trace of teamviewer from console: kirokko ~ $ teamviewer Init... Checking setup... Launching TeamViewer... fixme:service:scmdatabase_autostart_services Auto-start service L"MountMgr" failed to start: 2 fixme:service:scmdatabase_autostart_services Auto-start service L"PlugPlay" failed to start: 2 fixme:actctx:parse_depend_manifests Could not find dependent assembly L"Microsoft.Windows.Common-Controls" (6.0.0.0) fixme:heap:HeapSetInformation (nil) 1 (nil) 0 fixme:ole:CoInitializeSecurity ((nil),-1,(nil),(nil),0,3,(nil),0,(nil)) - stub! fixme:heap:HeapSetInformation (nil) 1 (nil) 0 fixme:process:SetProcessShutdownParameters (00000100, 00000000): partial stub. fixme:resource:GetGuiResources (0xffffffff,0): stub fixme:win:EnumDisplayDevicesW ((null),0,0x32dc60,0x00000000), stub! fixme:win:EnumDisplayDevicesW (L"\\\\.\\DISPLAY1",0,0x32d918,0x00000000), stub! fixme:win:EnumDisplayDevicesW ((null),1,0x32dc60,0x00000000), stub! fixme:winhttp:WinHttpDetectAutoProxyConfigUrl discovery via DHCP not supported fixme:msg:ChangeWindowMessageFilter 233 00000001 fixme:msg:ChangeWindowMessageFilter 4a 00000001 fixme:msg:ChangeWindowMessageFilter 407 00000001 fixme:msg:ChangeWindowMessageFilter 49 00000001 fixme:bitmap:CreateBitmapIndirect planes = 0 fixme:bitmap:CreateBitmapIndirect planes = 0 fixme:wtsapi:WTSRegisterSessionNotification Stub 0x1005a 0x00000000 err:ole:marshal_object couldn't get IPSFactory buffer for interface {00000131-0000-0000-c000-000000000046} err:ole:marshal_object couldn't get IPSFactory buffer for interface {00000122-0000-0000-c000-000000000046} err:ole:StdMarshalImpl_MarshalInterface Failed to create ifstub, hres=0x80040155 err:ole:CoMarshalInterface Failed to marshal the interface {00000122-0000-0000-c000-000000000046}, 80040155 fixme:msg:ChangeWindowMessageFilter c04f 00000001 fixme:richedit:ME_HandleMessage EM_SETFONTSIZE: stub fixme:dbghelp:elf_search_auxv can't find symbol in module wine: Unhandled page fault on read access to 0xffffffff at address 0xf7585c5a (thread 0009), starting debugger... err:seh:start_debugger Couldn't start debugger ("winedbg --auto 8 5552") (2) Read the Wine Developers Guide on how to set up winedbg or another debugger What's the problem? The same problem was when I had Ubuntu 12.10 installed, then the same problem was when I installed Mint 14 KDE (Kubuntu 12.10). Now I moved to Kubuntu 13.04 and the problem still exists.

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• One National Team One Event &ndash; SharePoint Saturday Kansas City

  - by MOSSLover

  I wasn’t expect to run an event from 1,000 miles away, but some stuff happened you know like it does and I opted in.  It was really weird, because people asked why are you living in NJ and running Kansas City?  I did move, but it was like my baby and Karthik didn’t have the ability to do it this year.  I found it really challenging, because I could not physically be in Kansas City.  At first I was freaking out and Lee Brandt, Brian Laird, and Chris Geier offered to help.  Somehow I couldn’t come the day of the event.  Time-wise it just didn’t work out.  I could do all the leg work prior to the event, but weekends just were not good.  I was going to be in DC until March or April on the weekdays, so leaving that weekend was too tough.  As it worked out Lee was my eyes and ears for the venue.  Brian was the sponsor and prize box coordinator if anyone needed to send items.  Lee also helped Brian the day of the event move all the boxes.  I did everything we could do electronically, such as get the sponsors coordinate with Michael Lotter on invoicing and getting the speakers, posting the submissions, budgeting the money, setting up a speaker dinner by phone, plus all that other stuff you do behind the scenes.  Chris was there to help Lee and Brian the day of the event and help us out with the speaker dinner.  Karthik finally got back from India and he was there the night before getting the folders together and the signs and stuffing it all.  Jason Gallicchio also helped me out (my cohort for SPS NYC) as he did the schedule and helped with posting the speakers abstracts and so did Chris Geier by posting the bios.  The lot of them enlisted a few other monkeys to help out.  It was the weirdest thing I’ve ever seen, but it worked.  Around 100+ attendees ended up showing and I hear it was  a great event.  Jason, Michael, Chris, Karthik, Brian, and Lee are not all from the same area, but they helped me out in bringing this event together.  It was a national SharePoint Saturday team that brought together a specific local event for Kansas City.  It’s like a metaphor for the entire SharePoint Community.  We help our own kind out we don’t let me fail.  I know Lee and Brian aren’t technically SharePoint People they are honorary SharePoint Community Members.  Thanks everyone for the support and help in bringing this event together.  Technorati Tags: SharePoint Saturday,SPS KC,SharePoint,SharePoint Saturday Kanas City,Kansas City

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• Translate Languages in IE 8 with Bing Translator

  - by Asian Angel

  Do you need side by side or hover language translations while browsing? Then join us as we look at the Bing Translator accelerator for Internet Explorer 8. Note: This article is geared towards those who may not have used this accelerator before or declined to “add it” when setting up IE 8. Using Bing Translator Once you have clicked on Add to Internet Explorer and confirmed the installation your new accelerator is ready to use. For our example we chose a Norwegian news article. Right-click within the webpage to access the context menu entry for translating. Depending on the originating language, you may want to go ahead and set it manually before beginning the translation. The translation will be opened in a new tab… Note: The same entry can also be accessed through the All Accelerators listing. There are four settings available for viewing your translations: side by side, top/bottom, original with hover translation, & translation with hover original. First a look at the side by side view. When maximized the window area will be divided 50/50 and as you hover your mouse or scroll in one side the same action will occur simultaneously in the other side. The top/bottom view. As above browser actions occur simultaneously in both sections. The original with hover translation view. Especially helpful if you are studying a new language and want to check your level of understanding for the original language. The translation with original hover view. Four different viewing options make it easy to find the one that best suits your needs. Conclusion If you need a convenient way to translate between languages in Internet Explorer 8, then the Bing Translator accelerator just might be what you have been looking for. Links Add the Bing Translator accelerator to Internet Explorer 8 Similar Articles Productive Geek Tips Quickly Translate Text to Another Language in Word 2007Add Google Translation Power to FirefoxTranslate Foreign Website Text to your Native LanguageAuto Translate Text in Google ChromeView Word Definitions in IE 8 with the Define with Bing Accelerator TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips HippoRemote Pro 2.2 Xobni Plus for Outlook All My Movies 5.9 CloudBerry Online Backup 1.5 for Windows Home Server 24 Million Sites Windows Media Player Glass Icons (icons we like) How to Forecast Weather, without Gadgets Outlook Tools, one stop tweaking for any Outlook version Zoofs, find the most popular tweeted YouTube videos Video preview of new Windows Live Essentials

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• Perform Unit Conversions with the Windows 7 Calculator

  - by Matthew Guay

  Want to easily convert area, volume, temperature, and many other units?  With the Calculator in Windows 7, it’s easy to convert most any unit into another. The New Calculator in Windows 7 Calculator received a visual overhaul in Windows 7, but at first glance it doesn’t seem to have any new functionality.  Here’s Windows 7’s Calculator on the left, with Vista’s calculator on the right.   But, looks can be deceiving.  Window’s 7’s calculator has lots of new exciting features.  Let’s try them out.  Simply type Calculator in the start menu search. To uncover the new features, click the View menu.  Here you can select many different modes, including Unit Conversion mode which we will look at. When you select the Unit Conversion mode, the Calculator will expand with a form on the left side. This conversions pane has 3 drop-down menus.  From the top one, select the type of unit you want to convert. In the next two menus, select which values you wish to convert to and from.  For instance, here we selected Temperature in the first menu, Degrees Fahrenheit in the second menu, and Degrees Celsius in the third menu. Enter the value you wish to convert in the From box, and the conversion will automatically appear in the bottom box. The Calculator contains dozens of conversion values, including more uncommon ones.  So if you’ve ever wanted to know how many US gallons are in a UK gallon, or how many knots a supersonic jet travels in an hour, this is a great tool for you!   Conclusion Windows 7 is filled with little changes that give you an all-around better experience in Windows to help you work more efficiently and productively.  With the new features in the Calculator, you just might feel a little smarter, too! Similar Articles Productive Geek Tips Add Windows Calculator to the Excel 2007 Quick Launch ToolbarEnjoy Quick & Easy Unit Conversion with Convert for WindowsCalculate with Qalculate on LinuxDisable the Annoying “This device can perform faster” Balloon Message in Windows 7Get stats on your Ruby on Rails code TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips DVDFab 6 Revo Uninstaller Pro Registry Mechanic 9 for Windows PC Tools Internet Security Suite 2010 Install, Remove and HIDE Fonts in Windows 7 Need Help with Your Home Network? Awesome Lyrics Finder for Winamp & Windows Media Player Download Videos from Hulu Pixels invade Manhattan Convert PDF files to ePub to read on your iPad

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• Facebook Sponsored Results: Is It Getting Results?

  - by Mike Stiles

  Social marketers who like to focus on the paid aspect of the paid/earned hybrid Facebook represents may want to keep themselves aware of how the network’s new Sponsored Results ad product is performing. The ads, which appear when a user conducts a search from the Facebook search bar, have only been around a week or so. But the first statistics coming out of them are not bad. Marketer Nanigans says click-through rates on the Sponsored Results have been nearly 23 times better than regular Facebook ads. Some click-through rates have even gone over 3%. Just to give you some perspective, a TechCrunch article points out that’s the same kind of click-through rates that were being enjoyed during the go-go dot com boom of the 90’s. The average across the Internet in its entirety is now somewhere around .3% on a good day, so a 3% number should be enough to raise an eyebrow. Plus the cost-per-click price is turning up 78% lower than regular Facebook ads, so that should raise the other eyebrow. Marketers have gotten pretty used to being able to buy ads against certain keywords. Most any digital property worth its salt that sells ads offers this, and so does Facebook with its Sponsored Results product. But the unique prize Facebook brings to the table is the ability to also buy based on demographic and interest information gleaned from Facebook user profiles. With almost 950 million logging in, this is exactly the kind of leveraging of those users conventional wisdom says is necessary for Facebook to deliver on its amazing potential. So how does the Facebook user fit into this? Notorious for finding out exactly where sponsored marketing messages are appearing and training their eyeballs to avoid those areas, will the Facebook user reject these Sponsored Results? Well, Facebook may have found an area in addition to the News Feed where paid elements can’t be avoided and will be tolerated. If users want to read their News Feed, and they do, they’re going to see sponsored posts. Likewise, if they want to search for friends or Pages, and they do, they’re going to see Sponsored Results. The paid results are clearly marked as such. As long as their organic search results are not tainted or compromised, they will continue using search. But something more is going on. The early click-through rate numbers say not only do users not mind seeing these Sponsored Results, they’re finding them relevant enough to click on. And once they click, they seem to be liking what they find, with a reported 14% higher install rate than Marketplace Ads. It’s early, and obviously the jury is still out. But this is a new social paid marketing opportunity that’s well worth keeping an eye on, and that may wind up hitting the trifecta of being effective for the platform, the consumer, and the marketer.

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• POP Forums v9 Beta 1 for ASP.NET MVC 3 posted to CodePlex!

  - by Jeff

  As promised, I posted a beta build of my forum app for ASP.NET MVC 3. Get the new goodies here: http://popforums.codeplex.com/releases/view/58228 This is the first beta for the ASP.NET MVC 3 version of POP Forums. It is nearly feature complete, and ready for testing and feedback. For previous release notes, look here, here and here.Check out the live preview: http://preview.popforums.com/ForumsSetup instructions are on the home page of this project. The new hotness in the beta, or what has been done since the last preview: All views converted to use Razor E-mail subscription/notification of new posts New post indicators/mark read buttons Permalinks to posts Jump to newest post (from new post indicators) Recent topics Favorite topics Moderator functions for topics (pin/close/delete, plus move and rename) Search, ported from v8. Not a ton of optimization here, or new unit testing, but the old version worked pretty well User posts (topics the user posted in) Forgot password Vanity items (signatures and avatars) Hide vanity items per user preference Some minor data caching where appropriate A little bit of UI refinement Lots-o-bug fixes Lots-o-unit tests What's next? The plan between now and the next beta is as follows: Continue working through features/tasks, and fix bugs as they're reported Integrate the forum into a real, production site Refine the UI Refactor as much as possible... the code organization is not entirely logical in some places After the second beta, a release candidate will follow, with a real "final" release after that. Subsequent releases should come relatively frequently and without a lot of risk. The trick in building this thing has been that it mostly tossed the previous WebForms version, which was all full of crusties. The time table for this is a little harder to pin down, as day jobs and families will have their effect. Other notes Refactoring will be a priority. As the features of MVC have evolved, so have my desires to use it in a fashion that makes things clear and easy to follow. I don't even know if anyone will ever start mucking around in the code, but on the off chance they do, I'd like what they find to not suck. Other nice-to-haves are builds to target Windows Azure and SQL CE. A nice setup UI would be super too. I think the ASP.NET MVC world has gone long enough without a decent forum.The biggest challenge that I've found is making the forum something that can be dropped in any app. While it does rope its views into an area, areas are mostly just routing details. I haven't thought of a clever way yet to limit dependency injection, for example, to just the forum bits. I mean, everyone should be using Ninject, but how realistic is that? ;)How much time and effort should you spend on POP Forums in its current state? Change is inevitable, but at this point I'm reasonably committed to not changing the database schema. I really think it will stay as-is. All bets are off for the various interfaces throughout the app, but the data should generally resist change. It's not even that different from v8, which was one of the original goals because I didn't want to rewrite SQL or introduce a new ORM or whatever. My point is that if you wanted to build a site around this today, even though it's not entirely functional, I think it's low risk in terms of data loss. I can't vouch for whether or not you know what you're doing.I've been having some chats with people lately about quoting posts, and honestly there has to be something better and straight forward. That continues to be a holy grail of mine, and some day, I hope to find it.Enjoy... it's starting to feel more real every day!

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• Extending NerdDinner: Adding Geolocated Flair

  - by Jon Galloway

  NerdDinner is a website with the audacious goal of “Organizing the world’s nerds and helping them eat in packs.” Because nerds aren’t likely to socialize with others unless a website tells them to do it. Scott Hanselman showed off a lot of the cool features we’ve added to NerdDinner lately during his popular talk at MIX10, Beyond File | New Company: From Cheesy Sample to Social Platform. Did you miss it? Go ahead and watch it, I’ll wait. One of the features we wanted to add was flair. You know about flair, right? It’s a way to let folks who like your site show it off in their own site. For example, here’s my StackOverflow flair: Great! So how could we add some of this flair stuff to NerdDinner? What do we want to show? If we’re going to encourage our users to give up a bit of their beautiful website to show off a bit of ours, we need to think about what they’ll want to show. For instance, my StackOverflow flair is all about me, not StackOverflow. So how will this apply to NerdDinner? Since NerdDinner is all about organizing local dinners, in order for the flair to be useful it needs to make sense for the person viewing the web page. If someone visits from Egypt visits my blog, they should see information about NerdDinners in Egypt. That’s geolocation – localizing site content based on where the browser’s sitting, and it makes sense for flair as well as entire websites. So we’ll set up a simple little callout that prompts them to host a dinner in their area: Hopefully our flair works and there is a dinner near your viewers, so they’ll see another view which lists upcoming dinners near them: The Geolocation Part Generally website geolocation is done by mapping the requestor’s IP address to a geographic area. It’s not an exact science, but I’ve always found it to be pretty accurate. There are (at least) three ways to handle it: You pay somebody like MaxMind for a database (with regular updates) that sits on your server, and you use their API to do lookups. I used this on a pretty big project a few years ago and it worked well. You use HTML 5 Geolocation API or Google Gears or some other browser based solution. I think those are cool (I use Google Gears a lot), but they’re both in flux right now and I don’t think either has a wide enough of an install base yet to rely on them. You might want to, but I’ve heard you do all kinds of crazy stuff, and sometimes it gets you in trouble. I don’t mean talk out of line, but we all laugh behind your back a bit. But, hey, it’s up to you. It’s your flair or whatever. There are some free webservices out there that will take an IP address and give you location information. Easy, and works for everyone. That’s what we’re doing. I looked at a few different services and settled on IPInfoDB. It’s free, has a great API, and even returns JSON, which is handy for Javascript use. The IP query is pretty simple. We hit a URL like this: http://ipinfodb.com/ip_query.php?ip=74.125.45.100&timezone=false … and we get an XML response back like this… <?xml version="1.0" encoding="UTF-8"?> <Response> <Ip>74.125.45.100</Ip> <Status>OK</Status> <CountryCode>US</CountryCode> <CountryName>United States</CountryName> <RegionCode>06</RegionCode> <RegionName>California</RegionName> <City>Mountain View</City> <ZipPostalCode>94043</ZipPostalCode> <Latitude>37.4192</Latitude> <Longitude>-122.057</Longitude> </Response> So we’ll build some data transfer classes to hold the location information, like this: public class LocationInfo { public string Country { get; set; } public string RegionName { get; set; } public string City { get; set; } public string ZipPostalCode { get; set; } public LatLong Position { get; set; } } public class LatLong { public float Lat { get; set; } public float Long { get; set; } } And now hitting the service is pretty simple: public static LocationInfo HostIpToPlaceName(string ip) { string url = "http://ipinfodb.com/ip_query.php?ip={0}&timezone=false"; url = String.Format(url, ip); var result = XDocument.Load(url); var location = (from x in result.Descendants("Response") select new LocationInfo { City = (string)x.Element("City"), RegionName = (string)x.Element("RegionName"), Country = (string)x.Element("CountryName"), ZipPostalCode = (string)x.Element("CountryName"), Position = new LatLong { Lat = (float)x.Element("Latitude"), Long = (float)x.Element("Longitude") } }).First(); return location; } Getting The User’s IP Okay, but first we need the end user’s IP, and you’d think it would be as simple as reading the value from HttpContext: HttpContext.Current.Request.UserHostAddress But you’d be wrong. Sorry. UserHostAddress just wraps HttpContext.Current.Request.ServerVariables["REMOTE_ADDR"], but that doesn’t get you the IP for users behind a proxy. That’s in another header, “HTTP_X_FORWARDED_FOR". So you can either hit a wrapper and then check a header, or just check two headers. I went for uniformity: string SourceIP = string.IsNullOrEmpty(Request.ServerVariables["HTTP_X_FORWARDED_FOR"]) ? Request.ServerVariables["REMOTE_ADDR"] : Request.ServerVariables["HTTP_X_FORWARDED_FOR"]; We’re almost set to wrap this up, but first let’s talk about our views. Yes, views, because we’ll have two. Selecting the View We wanted to make it easy for people to include the flair in their sites, so we looked around at how other people were doing this. The StackOverflow folks have a pretty good flair system, which allows you to include the flair in your site as either an IFRAME reference or a Javascript include. We’ll do both. We have a ServicesController to handle use of the site information outside of NerdDinner.com, so this fits in pretty well there. We’ll be displaying the same information for both HTML and Javascript flair, so we can use one Flair controller action which will return a different view depending on the requested format. Here’s our general flow for our controller action: Get the user’s IP Translate it to a location Grab the top three upcoming dinners that are near that location Select the view based on the format (defaulted to “html”) Return a FlairViewModel which contains the list of dinners and the location information public ActionResult Flair(string format = "html") { string SourceIP = string.IsNullOrEmpty( Request.ServerVariables["HTTP_X_FORWARDED_FOR"]) ? Request.ServerVariables["REMOTE_ADDR"] : Request.ServerVariables["HTTP_X_FORWARDED_FOR"]; var location = GeolocationService.HostIpToPlaceName(SourceIP); var dinners = dinnerRepository. FindByLocation(location.Position.Lat, location.Position.Long). OrderByDescending(p => p.EventDate).Take(3); // Select the view we'll return. // Using a switch because we'll add in JSON and other formats later. string view; switch (format.ToLower()) { case "javascript": view = "JavascriptFlair"; break; default: view = "Flair"; break; } return View( view, new FlairViewModel { Dinners = dinners.ToList(), LocationName = string.IsNullOrEmpty(location.City) ? "you" : String.Format("{0}, {1}", location.City, location.RegionName) } ); } Note: I’m not in love with the logic here, but it seems like overkill to extract the switch statement away when we’ll probably just have two or three views. What do you think? The HTML View The HTML version of the view is pretty simple – the only thing of any real interest here is the use of an extension method to truncate strings that are would cause the titles to wrap. public static string Truncate(this string s, int maxLength) { if (string.IsNullOrEmpty(s) || maxLength <= 0) return string.Empty; else if (s.Length > maxLength) return s.Substring(0, maxLength) + "..."; else return s; }   So here’s how the HTML view ends up looking: <%@ Page Title="" Language="C#" Inherits="System.Web.Mvc.ViewPage<FlairViewModel>" %> <%@ Import Namespace="NerdDinner.Helpers" %> <%@ Import Namespace="NerdDinner.Models" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Nerd Dinner</title> <link href="/Content/Flair.css" rel="stylesheet" type="text/css" /> </head> <body> <div id="nd-wrapper"> <h2 id="nd-header">NerdDinner.com</h2> <div id="nd-outer"> <% if (Model.Dinners.Count == 0) { %> <div id="nd-bummer"> Looks like there's no Nerd Dinners near <%:Model.LocationName %> in the near future. Why not <a target="_blank" href="http://www.nerddinner.com/Dinners/Create">host one</a>?</div> <% } else { %> <h3> Dinners Near You</h3> <ul> <% foreach (var item in Model.Dinners) { %> <li> <%: Html.ActionLink(String.Format("{0} with {1} on {2}", item.Title.Truncate(20), item.HostedBy, item.EventDate.ToShortDateString()), "Details", "Dinners", new { id = item.DinnerID }, new { target = "_blank" })%></li> <% } %> </ul> <% } %> <div id="nd-footer"> More dinners and fun at <a target="_blank" href="http://nrddnr.com">http://nrddnr.com</a></div> </div> </div> </body> </html> You’d include this in a page using an IFRAME, like this: <IFRAME height=230 marginHeight=0 src="http://nerddinner.com/services/flair" frameBorder=0 width=160 marginWidth=0 scrolling=no></IFRAME> The Javascript view The Javascript flair is written so you can include it in a webpage with a simple script include, like this: <script type="text/javascript" src="http://nerddinner.com/services/flair?format=javascript"></script> The goal of this view is very similar to the HTML embed view, with a few exceptions: We’re creating a script element and adding it to the head of the document, which will then document.write out the content. Note that you have to consider if your users will actually have a <head> element in their documents, but for website flair use cases I think that’s a safe bet. Since the content is being added to the existing page rather than shown in an IFRAME, all links need to be absolute. That means we can’t use Html.ActionLink, since it generates relative routes. We need to escape everything since it’s being written out as strings. We need to set the content type to application/x-javascript. The easiest way to do that is to use the <%@ Page ContentType%> directive. <%@ Page Language="C#" Inherits="System.Web.Mvc.ViewPage<NerdDinner.Models.FlairViewModel>" ContentType="application/x-javascript" %> <%@ Import Namespace="NerdDinner.Helpers" %> <%@ Import Namespace="NerdDinner.Models" %> document.write('<script>var link = document.createElement(\"link\");link.href = \"http://nerddinner.com/content/Flair.css\";link.rel = \"stylesheet\";link.type = \"text/css\";var head = document.getElementsByTagName(\"head\")[0];head.appendChild(link);</script>'); document.write('<div id=\"nd-wrapper\"><h2 id=\"nd-header\">NerdDinner.com</h2><div id=\"nd-outer\">'); <% if (Model.Dinners.Count == 0) { %> document.write('<div id=\"nd-bummer\">Looks like there\'s no Nerd Dinners near <%:Model.LocationName %> in the near future. Why not <a target=\"_blank\" href=\"http://www.nerddinner.com/Dinners/Create\">host one</a>?</div>'); <% } else { %> document.write('<h3> Dinners Near You</h3><ul>'); <% foreach (var item in Model.Dinners) { %> document.write('<li><a target=\"_blank\" href=\"http://nrddnr.com/<%: item.DinnerID %>\"><%: item.Title.Truncate(20) %> with <%: item.HostedBy %> on <%: item.EventDate.ToShortDateString() %></a></li>'); <% } %> document.write('</ul>'); <% } %> document.write('<div id=\"nd-footer\"> More dinners and fun at <a target=\"_blank\" href=\"http://nrddnr.com\">http://nrddnr.com</a></div></div></div>'); Getting IP’s for Testing There are a variety of online services that will translate a location to an IP, which were handy for testing these out. I found http://www.itouchmap.com/latlong.html to be most useful, but I’m open to suggestions if you know of something better. Next steps I think the next step here is to minimize load – you know, in case people start actually using this flair. There are two places to think about – the NerdDinner.com servers, and the services we’re using for Geolocation. I usually think about caching as a first attack on server load, but that’s less helpful here since every user will have a different IP. Instead, I’d look at taking advantage of Asynchronous Controller Actions, a cool new feature in ASP.NET MVC 2. Async Actions let you call a potentially long-running webservice without tying up a thread on the server while waiting for the response. There’s some good info on that in the MSDN documentation, and Dino Esposito wrote a great article on Asynchronous ASP.NET Pages in the April 2010 issue of MSDN Magazine. But let’s think of the children, shall we? What about ipinfodb.com? Well, they don’t have specific daily limits, but they do throttle you if you put a lot of traffic on them. From their FAQ: We do not have a specific daily limit but queries that are at a rate faster than 2 per second will be put in "queue". If you stay below 2 queries/second everything will be normal. If you go over the limit, you will still get an answer for all queries but they will be slowed down to about 1 per second. This should not affect most users but for high volume websites, you can either use our IP database on your server or we can whitelist your IP for 5$/month (simply use the donate form and leave a comment with your server IP). Good programming practices such as not querying our API for all page views (you can store the data in a cookie or a database) will also help not reaching the limit. So the first step there is to save the geolocalization information in a time-limited cookie, which will allow us to look up the local dinners immediately without having to hit the geolocation service.

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