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• Event sourcing and persistence

  - by jgauffin

  I'm reading up on event sourcing and have a question regarding persistence. I can still have a DB with all entities, right? Or should the events be replayed every time the application is started to get the latest version of each entity in the memory? Seems like a waste on larger systems (as in large amount of data)? The point with event sourcing is that I can can replay the events to populate a data store if required? (or analyze the data)

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• Bind to Collection Objects with Silverlight 3

  In this third part of the series we will continue to discuss Silverlight 3 data binding. This time however we ll cover more complex topics such as how to bind to collection objects. The fourth and fifth parts will cover how to deal with the validation during data binding not to mention the possible data conversion .... Test Drive the Next Wave of Productivity Find Microsoft Office 2010 and SharePoint 2010 trials, demos, videos, and more.

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• How difficult it is to develope Apps for Android and iOS? [on hold]

  - by netsetter

  I'm an experienced web developer in PHP, HTML, Javascript, MySQL, CSS and I'm running communities where people can register to be able to login and do some stuff. Now more and more people are requestion an App, I told them that I have no time and experience to develope Apps with many functions for such complex communities I am running, but then the users told me what would be enough for them and this sounds already simpler to me: An app to install on Android / iOS just to be able to login (+ autologin), so they appear always online in the community when they have internet connection. Then only 1 function like a counter of new activities regarding their user account (new messages, new replies, etc..), and if they click on the app then a browser window will open to read the info at the main website. So, what you think, it will be a big thing to develope such an app for the members? Is there a big diffrence between developing for Android and iOS? How to test the App if you don't have an Android or iOS phone in example?

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• Deduping your redundancies

  - by nospam(at)example.com (Joerg Moellenkamp)

  Robin Harris of Storagemojo pointed to an interesting article about about deduplication and it's impact to the resiliency of your data against data corruption on ACM Queue. The problem in short: A considerable number of filesystems store important metadata at multiple locations. For example the ZFS rootblock is copied to three locations. Other filesystems have similar provisions to protect their metadata. However you can easily proof, that the rootblock pointer in the uberblock of ZFS for example is pointing to blocks with absolutely equal content in all three locatition (with zdb -uu and zdb -r). It has to be that way, because they are protected by the same checksum. A number of devices offer block level dedup, either as an option or as part of their inner workings. However when you store three identical blocks on them and the devices does block level dedup internally, the device may just deduplicated your redundant metadata to a block stored just once that is stored on the non-voilatile storage. When this block is corrupted, you have essentially three corrupted copies. Three hit with one bullet. This is indeed an interesting problem: A device doing deduplication doesn't know if a block is important or just a datablock. This is the reason why I like deduplication like it's done in ZFS. It's an integrated part and so important parts don't get deduplicated away. A disk accessed by a block level interface doesn't know anything about the importance of a block. A metadata block is nothing different to it's inner mechanism than a normal data block because there is no way to tell that this is important and that those redundancies aren't allowed to fall prey to some clever deduplication mechanism. Robin talks about this in regard of the Sandforce disk controllers who use a kind of dedup to reduce some of the nasty effects of writing data to flash, but the problem is much broader. However this is relevant whenever you are using a device with block level deduplication. It's just the point that you have to activate it for most implementation by command, whereas certain devices do this by default or by design and you don't know about it. However I'm not perfectly sure about that ? given that storage administration and server administration are often different groups with different business objectives I would ask your storage guys if they have activated dedup without telling somebody elase on their boxes in order to speak less often with the storage sales rep. The problem is even more interesting with ZFS. You may use ditto blocks to protect important data to store multiple copies of data in the pool to increase redundancy, even when your pool just consists out of one disk or just a striped set of disk. However when your device is doing dedup internally it may remove your redundancy before it hits the nonvolatile storage. You've won nothing. Just spend your disk quota on the the LUNs in the SAN and you make your disk admin happy because of the good dedup ratio However you can just fall in this specific "deduped ditto block"trap when your pool just consists out of a single device, because ZFS writes ditto blocks on different disks, when there is more than just one disk. Yet another reason why you should spend some extra-thought when putting your zpool on a single LUN, especially when the LUN is sliced and dices out of a large heap of storage devices by a storage controller. However I have one problem with the articles and their specific mention of ZFS: You can just hit by this problem when you are using the deduplicating device for the pool. However in the specifically mentioned case of SSD this isn't the usecase. Most implementations of SSD in conjunction with ZFS are hybrid storage pools and so rotating rust disk is used as pool and SSD are used as L2ARC/sZIL. And there it simply doesn't matter: When you really have to resort to the sZIL (your system went down, it doesn't matter of one block or several blocks are corrupt, you have to fail back to the last known good transaction group the device. On the other side, when a block in L2ARC is corrupt, you simply read it from the pool and in HSP implementations this is the already mentioned rust. In conjunction with ZFS this is more interesting when using a storage array, that is capable to do dedup and where you use LUNs for your pool. However as mentioned before, on those devices it's a user made decision to do so, and so it's less probable that you deduplicating your redundancies. Other filesystems lacking acapability similar to hybrid storage pools are more "haunted" by this problem of SSD using dedup-like mechanisms internally, because those filesystem really store the data on the the SSD instead of using it just as accelerating devices. However at the end Robin is correct: It's jet another point why protecting your data by creating redundancies by dispersing it several disks (by mirror or parity RAIDs) is really important. No dedup mechanism inside a device can dedup away your redundancy when you write it to a totally different and indepenent device.

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• Outbound Traffic Logging on ASA 5520 possible?

  - by j2k4j

  Taking a look at the ASDM (6.4) for my ASA 5520, I get a nice summary of the traffic status, with items like "interface traffic usage", and "connections per second". This works well, but only shows the data for the last 5-6 minutes or so. Recently, I've been asked whether it's possible to pull up this same type of traffic data for a particular time in the past. (Such as: Find the traffic usage for a 3 minute period from date xx:xx:xx @ time xx:xx:xx) I've noticed that my ASA 5520 is logging the warning, errors, etc that it is processing. But traffic data is not logged (yet) according to my search through the ASA. Is logging the traffic data amounts (as wondered above) actually a possibility? Is there any way to find out the past data for traffic and such values? Thanks!

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• AppFabric named cache, what happens if you lose a cache host?

  - by Liam

  I'm getting my head around how app fabric clustering works and there's something I'm not sure about. Given a structure where we have one named cache, with two lead hosts and (say) three cache hosts and high availability turned off and the lead host(s) performing the management role. When one cache host goes down do you loose the data that was on that cache host? In this MSDN article it states: Data on the non-lead hosts would be lost (assuming high availability was not enabled), but the rest of the cluster could continue serving and storing data But I was unsure if redundancy is built into the system. Would you loose x amount of data or would one of the other cache hosts store this data also and pick up the slack?

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• OSXplanet: Updating cloud images

  - by Turgs

  Hello I'm using OSXplanet (which is a mac app based on xplanet) to view satellite and rendered images of the earth (or other planets) as the desktop background on my laptop. The images and data refresh regularly as data is updated, such as cyclones, clouds, weather, volcanoes, etc. I have Cloud Data set to refresh every 3 hours, but the resulting image never changes. By default, OSXplanet seems to be trying to get image data from Iowa State University. Can I modify OSXplanet to set it to pull cloud image data from a different server location listed on http://xplanet.sourceforge.net/clouds.php? Thanks Turgs

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• MySQL cluster: 20Tb x 3K tables

  - by ethrbunny

  Over the next 2-3 years we will be scaling up data collection for a project. As a result the amount of data will grow 10-fold. Our current MySQL installation can keep up with the 2Tb of data but for larger queries there is a fair amount of IOWait. Im investigating a migration to a clustered solution to spread out the IO but am wondering about NDB and what happens to data that doesn't get accessed very often. The impression I get from reading about MySQL cluster is that it relies on memory tables for most of the data. What happens with tables that don't get accessed very often (or at all)? And how does backup work? Can I use MYSQLDUMP or is there a better solution?

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• Linux using the link command

  - by Xavier

  Here it goes. I have a folder that contains a not so large amount of space called /data/backup but I have been told that if I link that folder (/data/backup) to an even bigger folder area like /bigdata/backup for example, that I will be able to execute backups to the /data/backup folder because it will be just a link but the data will be seen in both folders and the latter one (/bigdata/backup) will contain the backup results but it will show on both folders and since the /bigdata/backup has far more disk space then the backup will no longer fail because of space problems in the /data/backup one. Is this true? Thanks Xav

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• Cheap ways to do scaling ops in shader?

  - by Nick Wiggill

  I've got an extensive world terrain that uses vec3 for the vertex position attribute. That's good, because the terrain has endless gradations due to the use of floating point. But I'm thinking about how to reduce the amount of data uploaded to the GPU. For my terrain, which uses discrete / grid-based vertex positions in x and z, it's pretty clear that I can replace my vec3s (floats, really) with shorts, halving the per-vertex position attribute cost from 12 bytes each to 6 bytes. Considering I've got little enough other vertex data, and an enormous amount of terrain data to push into the world, it's a major gain. Currently in my code, one unit in GLSL shaders is equal to 1m in the world. I like that scale. If I move over to using shorts, though, I won't be able to use the same scale, as I would then have a very blocky world where every step in height is an entire metre. So I see these potential solutions to scale the positional data correctly once it arrives at the vertex shader stage: Use 10:1 scaling, i.e. 1 short unit = 1 decimetre in CPU-side code. Do a division by 10 in the vertex shader to scale incoming decimetre values back to metres. Arbirary (non-PoT) divisions tend to be slow, however. Use (some-power-of-two):1 scaling (eg. 8:1), which enables the use of a bitshift (eg. val >> 3) to do the division... not sure how performant this is in shaders, though. Not as intuitive to read values, but possibly quite a bit faster than div by a non-PoT value. Use a texture as lookup table. I've heard that this is really fast. Or whatever solutions others can offer to achieve the same results -- minimal vertex data with sensible scaling.

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• Postgres backup

  - by Abbass

  Hello, I have a Bacula script that does an automatic backup of a Postgres Database. The script makes two backups using (pg_dump) of the data base : The schema only and the data only. /usr/bin/pg_dump --format=c -s $dbname --file=$DUMPDIR/$dbname.schema.dump /usr/bin/pg_dump --format=c -a $dbname --file=$DUMPDIR/$dbname.data.dump The problem is that I can't figure out how to restore it with pg_restore. Do I need to create the database and the users before then restore the schema and finally the data. I did the following : pg_restore --format=c -s -C -d template1 xxx.schema.dump pg_restore --format=c -a -d xxx xxx.data.dump This first restore creates the database with emtpy tables but the second gives many error like this one : pg_restore: [archiver (db)] COPY failed: ERROR: insert or update on table "Table1" violates foreign key constraint "fkf6977a478dd41734" DETAIL: Key (contentid)=(1474566) is not present in table "Table23". Any ideas?

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• when should a database table be broken into multiple tables with relations?

  - by GSto

  I have an application that needs to store client data, and part of that is some data about their employer as well. Assuming that a client can only have one employer, and that the chance of people having identical employer data is slim to none, which schema would make more sense to use? Schema 1 Client Table: ------------------- id int name varchar(255), email varchar(255), address varchar(255), city varchar(255), state char(2), zip varchar(16), employer_name varchar(255), employer_phone varchar(255), employer_address varchar(255), employer_city varchar(255), employer_state char(2), employer_zip varchar(16) **Schema 2** Client Table ------------------ id int name varchar(255), email varchar(255), address varchar(255), city varchar(255), state char(2), zip varchar(16), Employer Table --------------------- id int name varchar(255), phone varchar(255), address varchar(255), city varchar(255), state char(2), zip varchar(16) patient_id int Part of me thinks that since are clearly two different 'objects' in the real world, seperating them out into two different tables makes sense. However, since a client will always have an employer, I'm also not seeing any real benefits to seperating them out, and it would make querying data about clients more complex. Is there any benefit / reason for creating two tables in a situation like this one instead of one?

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• Reporting what's not there

  It's easy to write queries that will show data in the database that matches a criteria. However, if no data in the database matches the criteria, it becomes more difficult. This article examines two different scenarios where it's necessary to create data in order to be able to report zero values in queries.

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• More Tables or More Databases?

  - by BuckWoody

  I got an e-mail from someone that has an interesting situation. He has 15,000 customers, and he asks if he should have a database for their data per customer. Without a LOT more data it’s impossible to say, of course, but there are some general concepts to keep in mind. Whenever you’re segmenting data, it’s all about boundary choices. You have not only boundaries around how big the data will get, but things like how many objects (tables, stored procedures and so on) that will be involved, if there are any cross-sections of data (do they share location or product information) and – very important – what are the security requirements? From the answer to these types of questions, you now have the choice of making multiple tables in a single database, or using multiple databases. A database carries some overhead – it needs a certain amount of memory for locking and so on. But it has a very clean boundary – everything from objects to security can be kept apart. Having multiple users in the same database is possible as well, using things like a Schema. But keeping 15,000 schemas can be challenging as well. My recommendation in complex situations like this is similar to a post on decisions that I did earlier – I lay out the choices on a spreadsheet in rows, and then my requirements at the top in the columns. I  give each choice a number based on how well it meets each requirement. At the end, the highest number wins. And many times it’s a mix – perhaps this person could segment customers into larger regions or districts or products, in a database. Within that database might be multiple schemas for the customers. Of course, he needs to query across all customers, that becomes another requirement. Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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• Search multiple tables

  - by gilden

  I have developed a web application that is used mainly for archiving all sorts of textual material (documents, references to articles, books, magazines etc.). There can be any given number of archive tables in my system, each with its own schema. The schema can be changed by a moderator through the application (imagine something similar to a really dumbed down version of phpMyAdmin). Users can search for anything from all of the tables. By using FULLTEXT indexes together with substring searching (fields which do not support FULLTEXT indexing) the script inserts the results of a search to a single table and by ordering these results by the similarity measure I can fairly easily return the paginated results. However, this approach has a few problems: substring searching can only count exact results the 50% rule applies to all tables separately and thus, mysql may not return important matches or too naively discards common words. is quite expensive in terms of query numbers and execution time (not an issue right now as there's not a lot of data yet in the tables). normalized data is not even searched for (I have different tables for categories, languages and file attatchments). My planned solution Create a single table having columns similar to id, table_id, row_id, data Every time a new row is created/modified/deleted in any of the data tables this central table also gets updated with the data column containing a concatenation of all the fields in a row. I could then create a single index for Sphinx and use it for doing searches instead. Are there any more efficient solutions or best practises how to approach this? Thanks.

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• What are the advantages of storing xml in a relational database?

  - by Chris

  I was poking around the AdventureWorks database today and I noticed that a number of tables (HumanResources.JobCandidate and Sales.Individual for example) have a column which is storing xml data. What I would to know is, what is the advantage of storing basically a database table row's worth of data in another table's column? Doesn't this make it difficult to query off of this information? Or is the assumption that the data won't need to be queried and just needs to be stored?

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• PHP Fingerprinting CMS Versions by their meta tags [migrated]

  - by Mud

  Hey guys I'm having some issues with the speed of my script. I'm a novice I know so getting past that - what suggestions would you have to speed up my script? I was originally just reading in the index.php and then searching the <head> of the page for an array of strings. Then I read about the get_meta_tags and went that way. Then I had issues with some sites having 300 redirects in place so I used curl to check the URL existed and to speed up things but it's still taking 5 minutes or so to execute. <?php function url_exist($url){ $c=curl_init(); curl_setopt($c,CURLOPT_URL,$url); curl_setopt($c,CURLOPT_HEADER,1); curl_setopt($c,CURLOPT_NOBODY,1); curl_setopt($c,CURLOPT_RETURNTRANSFER,1); curl_setopt($c,CURLOPT_FRESH_CONNECT,1); if(!curl_exec($c)){ return false; }else{ return true; } curl_close($c); } function checkVersion($url){ $tags = get_meta_tags($url); if (is_array($tags) && array_key_exists('generator', $tags)) { $v = "<span style='background-color:#7BF55D;color:#A3A0A0'>".$tags['generator']."</span"; }else{ $v="<span style='background-color:#F55D67;color:#A3A0A0'>Metatag not found!</span>"; } return $v; } $row = 1; echo "<table>"; if (($handle = fopen("url.csv", "r")) !== FALSE) { while (($data = fgetcsv($handle, 1000, ",")) !== FALSE) { $num = count($data); $row++; for ($c=0; $c < $num; $c++) { if(url_exist($data[$c])){ echo "<tr><td>".$data[$c]."</td><td>".checkVersion($data[$c])."</td></tr>"; sleep(2); }else{ echo "<tr><td>".$data[$c]."</td><td><td><span style='background-color:#F55D5D;color:#A3A0A0'>URL not valid!<span></td></tr>"; } } } fclose($handle); } echo "</table>"; ?>

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• What&rsquo;s Wrong With This Code (#25)

  The goal: create an extension method that will make it easy to create FormCollection objects. The method is a helper for unit testing ASP.NET MVC code. public static FormCollection ToFormCollection(this object data) { var namesAndValues = data.GetType() .GetProperties() .WhereValueIsNotDefaultValue(data) .ToNameValueCollection(data); return new FormCollection(namesAndValues); } The extension method itself relies on a couple private extension...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• JPGDateChanger - Tool to Restore Last Modified Date for JPG Files

  JPGDateChanger is a tool that changes last modified date to the one stored in EXIF data

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• Windows Phone 7 Isolated Storage Explorer

  - by help.net

  WP7 Isolated Storage Explorer is a tool designed to help developers and testers interact with the isolated storage file for Silverlight Windows Phone 7 applications. The explorer can work both as a desktop application for testers or integrated in Visual Studio for developers. Whenever a WP7 application/project involves storing data locally the the device, it will be to the isolated storage file. A common difficulty is accessing the data for testing or rapidly restoring the application's data/state...(read more)

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• Information I need to know as a Java Developer [on hold]

  - by Woy

  I'm a java developer. I'm trying to get more knowledge to become a better programmer. I've listed a number of technologies to learn. Instead of what I've listed, what technologies would you suggest to learn as well for a Junior Java Developer? I realize, there's a lot of things to study. Java: - how a garbage collector works - resource management - network programming - TCP/IP HTTP - transactions, - consistency: interfaces, classes collections, hash codes, algorithms, comp. complexity concurrent programming: synchronizing, semafores steam management metability: thread-safety byte code manipulations, reflections, Aspect-Oriented Programming as base to understand frameworks such as Spring etc. Web stack: servlets, filters, socket programming Libraries: JDK, GWT, Apache Commons, Joda-Time, Dependency Injections: Spring, Nano Tools: IDE: very good knowledge - debugger - profiler - web analyzers: Wireshark, firebugs - unit testing SQL/Databases: Basics SELECTing columns from a table Aggregates Part 1: COUNT, SUM, MAX/MIN Aggregates Part 2: DISTINCT, GROUP BY, HAVING + Intermediate JOINs, ANSI-89 and ANSI-92 syntax + UNION vs UNION ALL x NULL handling: COALESCE & Native NULL handling Subqueries: IN, EXISTS, and inline views Subqueries: Correlated ITH syntax: Subquery Factoring/CTE Views Advanced Topics Functions, Stored Procedures, Packages Pivoting data: CASE & PIVOT syntax Hierarchical Queries Cursors: Implicit and Explicit Triggers Dynamic SQL Materialized Views Query Optimization: Indexes Query Optimization: Explain Plans Query Optimization: Profiling Data Modelling: Normal Forms, 1 through 3 Data Modelling: Primary & Foreign Keys Data Modelling: Table Constraints Data Modelling: Link/Corrollary Tables Full Text Searching XML Isolation Levels Entity Relationship Diagrams (ERDs), Logical and Physical Transactions: COMMIT, ROLLBACK, Error Handling

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• What are the Starting Games I need to make?[Best steps for a beginner Game Developer?] [closed]

  - by Man With Steel Nerves...

  Possible Duplicate: What are good games to “earn your wings” with? Hai, I'm new to the genre "Creating Games".Previously i had done only porting.I need some suggestion's for making a game. What are the basic game logics i need to start with? - Should i write Tic-Tac-Toe game? - Actually this seem very basic to me. I'm totally confused on where to start with.I like to create big games but after starting i feel the game is too heavy to handle. Can any one list out the basic needs of a Game Play programmer? I don't mind using any platform (Flash,c++,objective-c) but i need to know what are the game logic's i need to know before i start a big game.

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• What simple offline GUI database should I use for this application?

  - by gcc

  I am looking an open source application. Application should have : * database support ( create two or three table ) * GUI ( what I have created should be seen ) Example : Assume that I have created a table ; X_table : | A | B | C | D | After creating table, I am loading data | A | B | C | D | | 1 | 11 | b | f | - | 3 | 12 | a | o | - data | 4 | 13 | r | o | - When I am opening application not for loading data, I want see data in graphical interface. Are there any open source application which have above feature ? Application can be so simple, * no internet connection * support only one database * static table creation ( once created never changed ) Application can be run Ubuntu 12.04 and/or Windows. In other words, I am wanting database viewer and editor. EDIT: I should load pdf file, image etc. or give path of the file to the application. This link can be reference to my question . ( Interface should be like this, just a list )

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• WCF RIA Services - Hands On Lab

  At the keynote for the Silverlight 4 Launch alongside Scott Guthrie I demonstrated (minute 28 to minute 38) how to build a Silverlight 4 application using WCF RIA Services and the new Visual Studio 2010 tooling. The application I built is an online book store to rival the big boys OK, well, maybe not the big boys but you get the idea. As promised I am elaborating on the presentation and breaking down the steps to create the application here. I included the starter solution and the completed...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• How do I count Internal Logical Files (ILF) and External Inputs (EI) for a dynamic form entry page?

  - by DmytroL

  Assuming I have an applicant information entry screen, the number and types of fields on which can be defined by the system administrator, how do I go about counting the number of Internal Logical Files (ILFs) and Data Element Types (DETs) for the related data functions? So far I have come up with something like this: ILF #1 (control information): Field Metadata, 1 RET, ~3 DET (name, type, mandatory) ILF #2 (business data): Applicant Data, most likely 1 RET, but how many DET? Of course I could count it as 2 DET (Field ref, Value), but I am not sure that would be correct And when it comes to an External Input (EI), say, "Add New Applicant", things become even more complicated, because the number of DET corresponding to the user-editable fields is totally dependent on the control information in ILF #1, and I am out of ideas here... Anyone fancy to help with that? Thanks in advance!

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