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  • How to communicate between Client and Server in a Client-Server Application?

    - by Sanoj
    I would like to implement an Client-Server Application, where the business-logic, security validations and a database are at the server and the user interface are at the client. I would like to implement clients in different languages i.e. one in WPF/.NET, one Swing/Java , one in Android/Java and maybe one HTML/JavaScript client. The server will be on Internet, so I would like to be able to have encrypted communication. The client will send some lists of items to be added to the database, or update items, and do some transactions. The server will check if the items are already updated by another client, or update the item, add new items or delete items. How do I solve the communication between clients and the server in such a system? I have been thinking about: http/https webserver, and sending messages in JSON or XML and use Web Sockets for bi-directional communication. Use http in a RESTful way, except when WebSockets are needed. But I guess there are better solutions for native desktop applications than http? CORBA - I have just heard about it, and it's old and complex. Not much talk about it these days. XMPP/Jabber - I have just heard about it and I don't know if it fits me at all. EJabberd seams to be a popular implementation. AMQP - I have just heard about it and I don't know if it fits me at all. RabbitMQ seams to be a popular implementation. Windows Communication Foundation, Java RMI, Java Message Service - but are they language independent? I guess some of these alternatives are on different levels, maybe I can have i.e xmpp or amqp in web sockets over https? What technologys are used for this problem in companies today? and what is recommended to use? I have no experience of them other than webservers and http. Please give me some guidance in this jungle. What are the pros and cons of these technologies in my situation?

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  • What is cached on a client machine when using https.

    - by TroyP
    I have an application that is working on https for everybody and on http for all but two users. The two users get a JavaScript error when trying to "edit" a page while on http but can edit the page on https. The problem is for occurs for both IE6 and FF3.6 for one of these users. Others have no problem using any browser. I have used Charles Proxy to look at the server response and no request is being made to https when on http and all browser requests return successfully. I have cleared all caches known to me on the clients (browser, jvm). Are http and https caches stored in different locations on the clients computers. Could a cached encrypted file be being read on the unencrypted port.

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  • Can sphinx be used over cassandra?

    - by Mickey Shine
    I am planning to build a cassandra store system and also I need a full-text(Chinese) system too. Can sphinx be used on cassandra? (sphinx supports xml format but I am not going to use it, cause it is slow and much of time are spent on xml parsing). Or you can share your experiences if you have ever built a full-text searching system over cassandra. Thank you

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  • See if any application has a DLL from the GAC loaded

    - by rwmnau
    I'm trying to deploy new copies of my DLL to the GAC on remote servers, but I need to identify if any processes currently running have a loaded copy of the DLL I'm replacing - I'd like to restart them, or at least tell the user. For example, Biztalk seems to load the DLLs it needs the first time they're used, and then replacing them keeps the old copy in memory until the Host Instances are restarted - something I could easily do as part of my deployment. Is there a way to tell using .NET which processes have loaded a particular DLL from the GAC? UPDATE: Some further investigation shows that both Process Explorer has this functionality, and another Sysinternals tool, ListDLL, does exactly what I want to be able to do. I'd like to know how they do it, since I'd love to replicate this functionality in my application without having to include and screen-scrape ListDLL (if that's even allowed inside the license).

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  • Cross-database transactions from one SP

    - by Michael Bray
    I need to update multiple databases with a few simple SQL statement. The databases are configurared in SQL using 'Linked Servers', and the SQL versions are mixed (SQL 2008, SQL 2005, and SQL 2000). I intend to write a stored procedure in one of the databases, but I would like to do so using a transaction to make sure that each database gets updated consistently. Which of the following is the most accurate: Will a single BEGIN/COMMIT TRANSACTION work to guarantee that all statements across all databases are successful? Will I need multiple BEGIN TRANSACTIONS for each individual set of commands on a database? Are transactions even supported when updating remote databases? I would need to execute a remote SP with embedded transaction support. Note that I don't care about any kind of cross-database referential integrity; I'm just trying to update multiple databases at the same time from a single stored procedure if possible. Any other suggestions are welcome as well. Thanks!

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  • Would dynamically created JavaScript files be cached?

    - by venksster
    So my application uses a LOT of js files. thats a lot of http requests. I decided to combine them dynamically at the server in packs of 3-4 files clubbed by functionality. My client side request is: ...script type="text/javascript" src="http://mydomain.com/core-js.php" ... My server side does: --core-js.php-- header("Content-type: application/x-javascript"); include_once('file1.js'); include_once('file2.js'); include_once('file3.js'); include_once('file4.js'); I am setting a far future expire header on core-js.php. My question is, would core-js.php be cached at the client side? If it would be, could someone please explain how? Thanks!

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  • Using installshield to replace a same-versioned DLL in the GAC

    - by Kevin
    We recently put out an update of one of our apps with a "test" DLL from a third party. The third party does not update their assembly versions on the dll's, only the file versions, so multiple apps can reference different "versions" of it. However, the GAC still allows us to keep the newest version, because it also checks the file version which is always updated. What happened is we were not ready to release this DLL, but it got out there on some customer machines. I would like to put our current live version back out there, but it has an older file version (and the same assembly version) as the test DLL. We have multiple apps referencing this DLL, so I can't simply delete it and drop in the new one. Is there a way to replace the DLL in the GAC? I'm using installshield 2009. Perhaps some sort of custom action upon install?

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  • De-normalization alternative to specific MYSQL problem?

    - by Booker
    I am facing quite a specific optimization problem. I currently have 4 normalized tables of data. Every second, possibly thousands of users will pull down up-to-date info from these tables using AJAX. The thing is that I can predict relatively easily which subset of data they need... The most recent 100 or so entries in those 4 normalized tables. I have been researching de-normalization... but feel that perhaps there is an easier solution. I was thinking that I could somehow every second run one sql query to condense the needed info, store it in a temp cached table and then have all of the user queries just draw from this. This will allow the complex join of 4 tables to only be run once, and then from there the users just need to do a simple lookup from the cached table. I really don't know if this is feasible. Comments on this or any other suggestions would be much appreciated. Thanks!

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  • Generate image with Drupal imagecache before using imagecache_create_path & getimagesize

    - by ozke
    Hi guys, I'm using imagecache_create_path() and getimagesize() to get the path of a imagecache-generated image and its dimensions. However, if it's the first time we access the page that image doesn't exist yet and imagecache_create_path doesn't generate it either. Here's the code: // we get the image path from a preset (always return the path even if the file doesn't exist) $small_image_path = imagecache_create_path('gallery_image_small', $image["filepath"]); // I get the image dimensions (only if the file exists already) $data_small = list($width, $height, $type, $image_attributes) = @getimagesize($small_image_path); Is there any API method to get the path AND generate the file? In other words, can I generate the image (using a preset) from PHP without showing it in the browser? Thank you in advance

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  • Why isn't Hadoop implemented using MPI?

    - by artif
    Correct me if I'm wrong, but my understanding is that Hadoop does not use MPI for communication between different nodes. What are the technical reasons for this? I could hazard a few guesses, but I do not know enough of how MPI is implemented "under the hood" to know whether or not I'm right. Come to think of it, I'm not entirely familiar with Hadoop's internals either. I understand the framework at a conceptual level (map/combine/shuffle/reduce and how that works at a high level) but I don't know the nitty gritty implementation details. I've always assumed Hadoop was transmitting serialized data structures (perhaps GPBs) over a TCP connection, eg during the shuffle phase. Let me know if that's not true.

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  • Is there an use case for non-blocking receive when I have threads?

    - by Gabriel Šcerbák
    I know non-blocking receive is not used as much in message passing, but still some intuition tells me, it is needed. Take for example GUI event driven applications, you need some way to wait for a message in a non-blocking way, so your program can execute some computations. One of the ways to solve this is to have a special thread with message queue. Is there some use case, where you would really need non-blocking receive even if you have threads?

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  • Is AMQP suitable as both an intra and inter-machine software bus?

    - by Bwooce
    I'm trying to get my head around AMQP. It looks great for inter-machine (cluster, LAN, WAN) communication between applications but I'm not sure if it is suitable (in architectural, and current implementation terms) for use as a software bus within one machine. Would it be worth pulling out a current high performance message passing framework to replace it with AMQP, or is this falling into the same trap as RPC by blurring the distinction between local and non-local communication? I'm also wary of the performance impacts of using a WAN technology for intra-machine communications, although this may be more of an implementation concern than architecture. War stories would be appreciated.

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  • Database caching on a shared host

    - by tau
    Anyone have any ideas how to increase MySQL performance on a shared host? My question has less to do with overall database performance and more to do with simply retrieving user-submitted data. Currently my database will create caches at timed intervals, and then the PHP will selectively access the static files it needs. This has given me a noticeable performance boost, but I am worried about a time in which I have so much data that having to read in big files in PHP will actually be slower. I am just looking for ideas for shared hosting solutions; I am not going to get my own server anytime soon. Thanks!

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  • Decentralized synchronized secure data storage

    - by Alberich
    Introduction Hi, I am going to ask a question which seems utopic for me, but I need to know if there is a way to achieve what I need. And if not, I need to know why not. The idea Suppose I have a database structure, in MySql. I want to create some solution to allow anyone (no matter who, no matter where) to have a synchronized copy (updated clone) of this database (with its content) Well, and it is not going to be just one synchronized copy, it could (and should) be a multiple replication (supposing the basic, this means, for example, ten copies all over the world) And, the most important thing: It must be secure. By secure I mean only real-accepted transactions will be synchronized with all the others (no matter how many) database copies/clones. Note: Since it would be quite difficult to make the synchronization in real-time, I will design everything to make this feature dispensable. So it is not required. My auto-suggestion This is how I am thinking to manage it: Time identifiers and Updates checking: Every action (insert, update, delete...) will be stored as the action instruction itself, associated to the time identifier. [I think better than a DATETIME field, it'll be an INT one, with the number of miliseconds passed from 1st january 2013 on, for example]. So each copy is going to ask to the "neighbour copy" for new actions done since last update, and execute them after checking they are allowed. Problem 1: the "neighbour copy" could be outdated too. Solution 1: do not ask just one neighbour, create a random list with some of the copies/clones and ask them for news (I could avoid the list and ask ALL the clones for updates, but this will be inefficient if clones number ascends too much). Problem 2: Real-time global synchronization is not active. What if... Someone at CLONE_ENTERPRISING inserts a row into TABLE. ... this row goes to every clone ... Someone at CLONE_FIXEMALL deletes this row. ... and at the same time, somewhere in an outdated clone ... Someone at CLONE_DROPOUT edits this row (now inexistent at the other clones) Solution 2: easy stuff, force a GLOBAL synchronization before doing any new "depending-on-third-data action" (edit, for example). This global synch. will be unnecessary when making an INSERT, for instance. Note: Well, someone could have some fun, and make the same insert in two clones... since they're not getting updated in real-time, this row will exist twice. But, it's the same as when we have one single database, in some needed cases we check if there is an existing same-row before doing the final action. Not a problem. Problem 3: It is possible to edit the code and do not filter actions, so someone could spread instructions to delete everything, or just make some trolling activity. This is not a problem, since good clones will always be somewhere. Those who got bad won't interest anymore. I really appreciate if you read. I know this is not the perfect solution, it has possibly hundred of holes, but it is my basic start. I will now appreciate anything you can teach me now. Thanks a lot. PS.: It could be that all this I am trying already exists and has its own name. Sorry for asking then (I'd anyway thank this name, if it exists)

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  • How to design a high-level application protocol for metadata syncing between devices and server?

    - by Jaanus
    I am looking for guidance on how to best think about designing a high-level application protocol to sync metadata between end-user devices and a server. My goal: the user can interact with the application data on any device, or on the web. The purpose of this protocol is to communicate changes made on one endpoint to other endpoints through the server, and ensure all devices maintain a consistent picture of the application data. If user makes changes on one device or on the web, the protocol will push data to the central repository, from where other devices can pull it. Some other design thoughts: I call it "metadata syncing" because the payloads will be quite small, in the form of object IDs and small metadata about those ID-s. When client endpoints retrieve new metadata over this protocol, they will fetch actual object data from an external source based on this metadata. Fetching the "real" object data is out of scope, I'm only talking about metadata syncing here. Using HTTP for transport and JSON for payload container. The question is basically about how to best design the JSON payload schema. I want this to be easy to implement and maintain on the web and across desktop and mobile devices. The best approach feels to be simple timer- or event-based HTTP request/response without any persistent channels. Also, you should not have a PhD to read it, and I want my spec to fit on 2 pages, not 200. Authentication and security are out of scope for this question: assume that the requests are secure and authenticated. The goal is eventual consistency of data on devices, it is not entirely realtime. For example, user can make changes on one device while being offline. When going online again, user would perform "sync" operation to push local changes and retrieve remote changes. Having said that, the protocol should support both of these modes of operation: Starting from scratch on a device, should be able to pull the whole metadata picture "sync as you go". When looking at the data on two devices side by side and making changes, should be easy to push those changes as short individual messages which the other device can receive near-realtime (subject to when it decides to contact server for sync). As a concrete example, you can think of Dropbox (it is not what I'm working on, but it helps to understand the model): on a range of devices, the user can manage a files and folders—move them around, create new ones, remove old ones etc. And in my context the "metadata" would be the file and folder structure, but not the actual file contents. And metadata fields would be something like file/folder name and time of modification (all devices should see the same time of modification). Another example is IMAP. I have not read the protocol, but my goals (minus actual message bodies) are the same. Feels like there are two grand approaches how this is done: transactional messages. Each change in the system is expressed as delta and endpoints communicate with those deltas. Example: DVCS changesets. REST: communicating the object graph as a whole or in part, without worrying so much about the individual atomic changes. What I would like in the answers: Is there anything important I left out above? Constraints, goals? What is some good background reading on this? (I realize this is what many computer science courses talk about at great length and detail... I am hoping to short-circuit it by looking at some crash course or nuggets.) What are some good examples of such protocols that I could model after, or even use out of box? (I mention Dropbox and IMAP above... I should probably read the IMAP RFC.)

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  • Recommended integration mechanism for bi-directional, authenticated, encrypted connection in C clien

    - by rcampbell
    Let me first give an example. Imagine you have a single server running a JVM application. This server keeps a collection of N equations, once for each client: Client #1: 2x Client #2: 1 + y Client #3: z/4 This server includes an HTTP interface so that random visitors can type https://www.acme.com/client/3 int their browsers and see the latest evaluated result of z/4. The tricky part is that either the client or the server may change the variable value at any time, informing the other party immediately. More specifically, Client #3 - a C app - can initially tell the server that z = 20. An hour later that same client informs the server that z = 23. Likewise the server can later inform the client that z = 28. As caf pointed out in the comments, there can be a race condition when values are changed by the client and server simultaneously. The solution would be for both client and server to send the operation performed in their message, which would need to be executed by the other party. To keep things simple, let's limit the operations to (commutative) addition, allowing us to disregard message ordering. For example, the client seeds the server with z = 20: server:z=20, client:z=20 server sends {+3} message (so z=23 locally) & client sends {-2} message (so z=18 locally) at the exact same time server receives {-2} message at some point, adds to his local copy so z=21 client receives {+3} message at some point, adds to his local copy so z=21 As long as all messages are eventually evaluated by both parties, the correct answer will eventually be given to the users of the client and server since we limited ourselves to commutative operations (addition of 3 and -2). This does mean that both client and server can be returning incorrect answers in the time it takes for messages to be exchanged and processed. While undesirable, I believe this is unavoidable. Some possible implementations of this idea include: Open an encrypted, always on TCP socket connection for communication Pros: no additional infrastructure needed, client and server know immediately if there is a problem (disconnect) with the other party, fairly straightforward (except the the encryption), native support from both JVM and C platforms Cons: pretty low-level so you end up writing a lot yourself (protocol, delivery verification, retry-on-failure logic), probably have a lot of firewall headaches during client app installation Asynchronous messaging (ex: ActiveMQ) Pros: transactional, both C & Java integration, free up the client and server apps from needing retry logic or delivery verification, pretty straightforward encryption, easy extensibility via message filters/routers/etc Cons: need additional infrastructure (message server) which must never fail, Database or file system as asynchronous integration point Same pros/cons as above but messier RESTful Web Service Pros: simple, possible reuse of the server's existing REST API, SSL figures out the encryption problem for you (maybe use RSA key a la GitHub for authentication?) Cons: Client now needs to run a C HTTP REST server w/SSL, client and server need retry logic. Axis2 has both a Java and C version, but you may be limited to SOAP. What other techniques should I be evaluating? What real world experiences have you had with these mechanisms? Which do you recommend for this problem and why?

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  • Is asp.net caching my sql results?

    - by Christian W
    I have the following method in an App_Code/Globals.cs file: public static XmlDataSource getXmlSourceFromOrgid(int orgid) { XmlDataSource xds = new XmlDataSource(); var ctx = new SensusDataContext(); SqlConnection c = new SqlConnection(ctx.Connection.ConnectionString); c.Open(); SqlCommand cmd = new SqlCommand(String.Format("select orgid, tekst, dbo.GetOrgTreeXML({0}) as Subtree from tblOrg where OrgID = {0}", orgid), c); var rdr = cmd.ExecuteReader(); rdr.Read(); StringBuilder sb = new StringBuilder(); sb.AppendFormat("&lt;node orgid=\"{0}\" tekst=\"{1}\"&gt;",rdr.GetInt32(0),rdr.GetString(1)); sb.Append(rdr.GetString(2)); sb.Append("&lt;/node&gt;"); xds.Data = sb.ToString(); xds.ID = "treedata"; rdr.Close(); c.Close(); return xds; } This gives me an XML-structure to use with the asp.net treeview control (I also use the CssFriendly extender to get nicer code) My problem is that if I logon on my pc with a code that gives me access on a lower level in the tree hierarchy (it's an orgianization hierarchy), it somehow "remembers" what level i logon at. So when my coworker tests from her computer with another code, giving access to another place in the tree, she get's the same tree as me. (The tree is supposed to show your own level and down.) I have added a html-comment to show what orgid it passes to the function, and the orgid passed is correct. So either the treeview caches something serverside, or the sqlquery caches it's result somehow... Any ideas? Sql function: ALTER function [dbo].[GetOrgTreeXML](@orgid int) returns XML begin RETURN (select org.orgid as '@orgid', org.tekst as '@tekst', [dbo].GetOrgTreeXML(org.orgid) from tblOrg org where (@orgid is null and Eier is null) or Eier=@orgid for XML PATH('NODE'), TYPE) end Extra code as requested: int orgid = int.Parse(Session["org"].ToString()); string orgname = context.Orgs.Where(q => q.OrgID == orgid).First().Tekst; debuglit.Text = String.Format("<!-- Id: {0} \n name: {1} -->", orgid, orgname); var orgxml = Globals.getXmlSourceFromOrgid(orgid); tvNavtree.DataSource = orgxml; tvNavtree.DataBind(); Where "debuglit" is a asp:Literal in the aspx file. EDIT: I have narrowed it down. All functions returns correct values. It just doesn't bind to it. I suspect the CssFriendly adapter to have something to do with it. I disabled the CssFriendly adapter and the problem persists... Stepping through it in debug it's correct all the way, with the stepper standing on "tvNavtree.DataBind();" I can hover the pointer over the tvNavtree.Datasource and see that it actually has the correct data. So something must be faulting in the binding process...

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  • Algorithms for modern hardware?

    - by Jurily
    Once again, I find myself with a set of broken assumptions. The article itself is about a 10x performance gain by modifying a proven-optimal algorithm to account for virtual memory: What good is an O(log2(n)) algorithm if those operations cause page faults and slow disk operations? For most relevant datasets an O(n) or even an O(n^2) algorithm, which avoids page faults, will run circles around it. Are there more such algorithms around? Should we re-examine all those fundamental building blocks of our education? What else do I need to watch out for when writing my own?

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  • How can I get a rails server to use the same databse that cucumber uses during a test?

    - by James
    The cucumber test first makes an entry in the database and posts a form to a second server. This second server does some processing in background and then hits the first app (where the test is being run) with some data that the cucumber test needs to know about. I've tried running the main server via script/server and script/server -e test while the cucumber test is running, but I can't seem to force the server to use the same database that cucumber is using when it runs its step definitions. That is, when the second server pushes some data to a controller in the main server, the main server doesn't know about any entries that cucumber has made in the database. How can I get cucumber and the main server to use the same database?

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