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• Slow XML-RPC in Windows 7 with XML-RPC.NET

  - by Emre Sahin

  I'm considering to use XML-RPC.NET to communicate with a Linux XML-RPC server written in Python. I have tried a sample application (MathApp) from Cook Computing's XML-RPC.NET but it took 30 seconds for the app to add two numbers within the same LAN with server. I have also tried to run a simple client written in Python on Windows 7 to call the same server and it responded in 5 seconds. The machine has 4 GB of RAM with comparable processing power so this is not an issue. Then I tried to call the server from a Windows XP system with Java and PHP. Both responses were pretty fast, almost instantly. The server was responding quickly on localhost too, so I don't think the latency arise from server. My googling returned me some problems regarding Windows' use of IPv6 but our call to server does include IPv4 address (not hostname) in the same subnet. Anyways I turned off IPv6 but nothing changed. Are there any more ways to check for possible causes of latency?

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• Ant build from Android-generated build file fails - how to fix?

  - by Eno

  Building our Android app from Ant fails with this error: [apply] [apply] UNEXPECTED TOP-LEVEL ERROR: [apply] java.lang.OutOfMemoryError: Java heap space [apply] at java.util.HashMap.<init>(HashMap.java:209) [apply] at java.util.HashSet.<init>(HashSet.java:86) [apply] at com.android.dx.ssa.Dominators.compress(Dominators.java:96) [apply] at com.android.dx.ssa.Dominators.eval(Dominators.java:132) [apply] at com.android.dx.ssa.Dominators.run(Dominators.java:213) [apply] at com.android.dx.ssa.DomFront.run(DomFront.java:84) [apply] at com.android.dx.ssa.SsaConverter.placePhiFunctions(SsaConverter.java:265) [apply] at com.android.dx.ssa.SsaConverter.convertToSsaMethod(SsaConverter.java:51) [apply] at com.android.dx.ssa.Optimizer.optimize(Optimizer.java:100) [apply] at com.android.dx.ssa.Optimizer.optimize(Optimizer.java:74) [apply] at com.android.dx.dex.cf.CfTranslator.processMethods(CfTranslator.java:269) [apply] at com.android.dx.dex.cf.CfTranslator.translate0(CfTranslator.java:131) [apply] at com.android.dx.dex.cf.CfTranslator.translate(CfTranslator.java:85) [apply] at com.android.dx.command.dexer.Main.processClass(Main.java:297) [apply] at com.android.dx.command.dexer.Main.processFileBytes(Main.java:276) [apply] at com.android.dx.command.dexer.Main.access$100(Main.java:56) [apply] at com.android.dx.command.dexer.Main$1.processFileBytes(Main.java:228) [apply] at com.android.dx.cf.direct.ClassPathOpener.processArchive(ClassPathOpener.java:245) [apply] at com.android.dx.cf.direct.ClassPathOpener.processOne(ClassPathOpener.java:130) [apply] at com.android.dx.cf.direct.ClassPathOpener.process(ClassPathOpener.java:108) [apply] at com.android.dx.command.dexer.Main.processOne(Main.java:245) [apply] at com.android.dx.command.dexer.Main.processAllFiles(Main.java:183) [apply] at com.android.dx.command.dexer.Main.run(Main.java:139) [apply] at com.android.dx.command.dexer.Main.main(Main.java:120) [apply] at com.android.dx.command.Main.main(Main.java:87) BUILD FAILED Ive tried giving Ant more memory by setting ANT_OPTS="-Xms256m -Xmx512m". (This build machine has 1Gb RAM). Do I just need more memory or is there anything else I can try?

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• MySQL Connection Timeout Issue - Grails Application on Tomcat using Hibernate and ORM

  - by gav

  Hi Guys I have a small grails application running on Tomcat in Ubuntu on a VPS. I use MySql as my datastore and everything works fine unless I leave the application for more than half a day (8 hours?). I did some searching and apparently this is the default wait_timeout in mysql.cnf so after 8 hours the connection will die but Tomcat won't know so when the next user tries to view the site they will see the connection failure error. Refreshing the page will fix this but I want to get rid of the error altogether. For my version of MySql (5.0.75) I have only my.cnf and it doesn't contain such a parameter, In any case changing this parameter doesn't solve the problem. This Blog Post seems to be reporting a similar error but I still don't fully understand what I need to configure to get this fixed and also I am hoping that there is a simpler solution than another third party library. The machine I'm running on has 256MB ram and I'm trying to keep the number of programs/services running to a minimum. Is there something I can configure in Grails / Tomcat / MySql to get this to go away? Thanks in advance, Gav From my Catalina.out; 2010-04-29 21:26:25,946 [http-8080-2] ERROR util.JDBCExceptionReporter - The last packet successfully received from the server was 102,906,722 milliseconds$ 2010-04-29 21:26:25,994 [http-8080-2] ERROR errors.GrailsExceptionResolver - Broken pipe java.net.SocketException: Broken pipe at java.net.SocketOutputStream.socketWrite0(Native Method) ... 2010-04-29 21:26:26,016 [http-8080-2] ERROR util.JDBCExceptionReporter - Already closed. 2010-04-29 21:26:26,016 [http-8080-2] ERROR util.JDBCExceptionReporter - Already closed. 2010-04-29 21:26:26,017 [http-8080-2] ERROR servlet.GrailsDispatcherServlet - HandlerInterceptor.afterCompletion threw exception org.hibernate.exception.GenericJDBCException: Cannot release connection at java.lang.Thread.run(Thread.java:619) Caused by: java.sql.SQLException: Already closed. at org.apache.commons.dbcp.PoolableConnection.close(PoolableConnection.java:84) at org.apache.commons.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.close(PoolingDataSource.java:181) ... 1 more

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• System Out Of Memory Exception in Production Server

  - by Sachin Gupta

  We have .net application installed on production server. It is using .net FrameWork 3.0 on windows server 2003 with RAM 4 GB. But there is a problem in application while running sometimes it throws system out of memory exception. I am very frustrating with this. Also I am unable to simulate the issue. I had checked all the possibilities which can cause the problem but didn’t get any thing which solve the issue I checked on production server event log found the Out Of Memory Exception also INVALID VIEW STATE logs are there. Look at the following event log which may help to find solutions. Exception information: Exception type: HttpException Exception message: Invalid viewstate. Request information: Request path: /zContest/ScriptResource.axd User: LisaA Is authenticated: True Authentication Type: Forms Thread information: Thread ID: 10 Is impersonating: True Stack trace: at System.Web.UI.Page.DecryptStringWithIV(String s, IVType ivType) at System.Web.UI.Page.DecryptString(String s) at System.Web.Handlers.ScriptResourceHandler.DecryptParameter(NameValueCollection queryString) at System.Web.Handlers.ScriptResourceHandler.ProcessRequestInternal(HttpResponse response, NameValueCollection queryString, VirtualFileReader fileReader) at System.Web.Handlers.ScriptResourceHandler.ProcessRequest(HttpContext context) at System.Web.Handlers.ScriptResourceHandler.System.Web.IHttpHandler.ProcessRequest(HttpContext context) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) ------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------------------------------------------ Event code: 3005 Event message: An unhandled exception has occurred. Process information: Process ID: 5388 Process name: w3wp.exe Exception information: Exception type: OutOfMemoryException Exception message: Exception of type 'System.OutOfMemoryException' was thrown. ------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------------------------------------------ Please help me out on this

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• Iterating through json object doesn't seem to work for me...

  - by Pandiya Chendur

  From a previous question on Stackoverflow Iterating through/Parsing JSON Object via JavaScript.... My json object doesn't seem get parsed.... here is my function function Iteratejsondata(HfJsonValue) { var jsonObj = eval('(' + HfJsonValue + ')'); for (var i = 0, len = HfJsonValue.length; i < len; ++i) { var employee = HfJsonValue[i]; document.write(employee.Emp_Name); } } employee.Emp_Name is undefined but when i give document.write(employee); i get this {"Table" : [{"Emp_Id" : "3","Identity_No" : "","Emp_Name" : "Jerome","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Supervisior","Desig_Description" : "Supervisior of the Construction","SalaryBasis" : "Monthly","FixedSalary" : "25000.00"},{"Emp_Id" : "4","Identity_No" : "","Emp_Name" : "Mohan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Acc ","Desig_Description" : "Accountant","SalaryBasis" : "Monthly","FixedSalary" : "200.00"},{"Emp_Id" : "5","Identity_No" : "","Emp_Name" : "Murugan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "150.00"},{"Emp_Id" : "6","Identity_No" : "","Emp_Name" : "Ram","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "120.00"},{"Emp_Id" : "7","Identity_No" : "","Emp_Name" : "Raja","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason","Desig_Description" : "Mason","SalaryBasis" : "Weekly","FixedSalary" : "135.00"},{"Emp_Id" : "8","Identity_No" : "","Emp_Name" : "Raja kumar","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason Helper","Desig_Description" : "Mason Helper","SalaryBasis" : "Weekly","FixedSalary" : "105.00"},{"Emp_Id" : "9","Identity_No" : "","Emp_Name" : "Lakshmi","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Mason Helper","Desig_Description" : "Mason Helper","SalaryBasis" : "Weekly","FixedSalary" : "100.00"},{"Emp_Id" : "10","Identity_No" : "","Emp_Name" : "Palani","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Carpenter","Desig_Description" : "Carpenter","SalaryBasis" : "Weekly","FixedSalary" : "200.00"},{"Emp_Id" : "11","Identity_No" : "","Emp_Name" : "Annamalai","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Carpenter","Desig_Description" : "Carpenter","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "12","Identity_No" : "","Emp_Name" : "David","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Fixer","Desig_Description" : "Steel Fixer","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "13","Identity_No" : "","Emp_Name" : "Chandru","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Fixer","Desig_Description" : "Steel Fixer","SalaryBasis" : "Weekly","FixedSalary" : "220.00"},{"Emp_Id" : "14","Identity_No" : "","Emp_Name" : "Mani","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Steel Helper","Desig_Description" : "Steel Helper","SalaryBasis" : "Weekly","FixedSalary" : "175.00"},{"Emp_Id" : "15","Identity_No" : "","Emp_Name" : "Karthik","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Fixer","Desig_Description" : "Wood Fixer","SalaryBasis" : "Weekly","FixedSalary" : "195.00"},{"Emp_Id" : "16","Identity_No" : "","Emp_Name" : "Bala","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Fixer","Desig_Description" : "Wood Fixer","SalaryBasis" : "Weekly","FixedSalary" : "185.00"},{"Emp_Id" : "17","Identity_No" : "","Emp_Name" : "Tamil arasi","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Wood Helper","Desig_Description" : "Wood Helper","SalaryBasis" : "Weekly","FixedSalary" : "185.00"},{"Emp_Id" : "18","Identity_No" : "","Emp_Name" : "Perumal","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Cook","Desig_Description" : "Cook","SalaryBasis" : "Weekly","FixedSalary" : "105.00"},{"Emp_Id" : "19","Identity_No" : "","Emp_Name" : "Andiappan","Address" : "Madurai","Date_Of_Birth" : "","Desig_Name" : "Watchman","Desig_Description" : "Watchman","SalaryBasis" : "Weekly","FixedSalary" : "150.00"}]} Any suggestion how to get this done...

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• LINQ to SQL : Too much CPU Usage: What happens when there are multiple users.

  - by soldieraman

  I am using LINQ to SQL and seeing my CPU Usage sky rocketting. See below screenshot. I have three questions What can I do to reduce this CPU Usage. I have done profiling and basically removed everything. Will making every LINQ to SQL statement into a compiled query help? I also find that even with compiled queries simple statements like ByID() can take 3 milliseconds on a server with 3.25GB RAM 3.17GHz - this will just become slower on a less powerful computer. Or will the compiled query get faster the more it is used? The CPU Usage (on the local server goes to 12-15%) for a single user will this multiply with the number of users accessing the server - when the application is put on a live server. i.e. 2 users at a time will mean 15*2 = 30% CPU Usage. If this is the case is my application limited to maximum 4-5 users at a time then. Or doesnt LINQ to SQL .net share some CPU usage.

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• maintaining a large list in python

  - by Oren

  I need to maintain a large list of python pickleable objects that will quickly execute the following algorithm: The list will have 4 pointers and can: Read\Write each of the 4 pointed nodes Insert new nodes before the pointed nodes Increase a pointer by 1 Pop nodes from the beginning of the list (without overlapping the pointers) Add nodes at the end of the list The list can be very large (300-400 MB), so it shouldnt be contained in the RAM. The nodes are small (100-200 bytes) but can contain various types of data. The most efficient way it can be done, in my opinion, is to implement some paging-mechanism. On the harddrive there will be some database of a linked-list of pages where in every moment up to 5 of them are loaded in the memory. On insertion, if some max-page-size was reached, the page will be splitted to 2 small pages, and on pointer increment, if a pointer is increased beyond its loaded page, the following page will be loaded instead. This is a good solution, but I don't have the time to write it, especially if I want to make it generic and implement all the python-list features. Using a SQL tables is not good either, since I'll need to implement a complex index-key mechanism. I tried ZODB and zc.blist, which implement a BTree based list that can be stored in a ZODB database file, but I don't know how to configure it so the above features will run in reasonable time. I don't need all the multi-threading\transactioning features. No one else will touch the database-file except for my single-thread program. Can anyone explain me how to configure the ZODB\zc.blist so the above features will run fast, or show me a different large-list implementation?

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• Need help troubleshooting why Solr wont start (or why solr admin page wont show)

  - by Camran

  I can't get Solr working. I have Jetty, and my server OS is Ubuntu 9.10. It is a VPS server. So, when I execute the java -jar start.jar everything seems fine. I even do a netstat to check if there are any listeners on the port before the start and after the start, and it seems solr is starting. However, I cant access the admin page. I have even turned off the firewall. Here is some info about my server: I have changed DocumentRoot to var/www/SV/ I have Apache2, PHP5, MySql installed I have "disabled" iptables firewall I have removed the htaccess files (I used them to passw protect my site under develop) I have installed JRE (NOT JDK) on my server. I use the "example" which comes with Solr, so I use Jetty as container on my Server. My Server has 768MB RAM Doing a java -version command shows this: java version "1.6.0_15" Java(TM) SE Runtime Environment (build 1.6.0_15-b03) Java HotSpot(TM) Client VM (build 14.1-b02, mixed mode) And in the terminal the last lines when executing start.jar is: May 29, 2010 1:30:03 PM org.apache.solr.core.SolrCore registerSearcher INFO: [] Registered new searcher Searcher@1dc64a5 main NOTE: Also before this last line, there is a line which makes me suspicious: Started SocketConnector @ 0.0.0.0:8983 // Should this be with leading zeros? Is there any ways you know to troubleshoot this? Memory issue maybe? Thanks

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• Using Hibernate's ScrollableResults to slowly read 90 million records

  - by at

  I simply need to read each row in a table in my MySQL database using Hibernate and write a file based on it. But there are 90 million rows and they are pretty big. So it seemed like the following would be appropriate: ScrollableResults results = session.createQuery("SELECT person FROM Person person") .setReadOnly(true).setCacheable(false).scroll(ScrollMode.FORWARD_ONLY); while (results.next()) storeInFile(results.get()[0]); The problem is the above will try and load all 90 million rows into RAM before moving on to the while loop... and that will kill my memory with OutOfMemoryError: Java heap space exceptions :(. So I guess ScrollableResults isn't what I was looking for? What is the proper way to handle this? I don't mind if this while loop takes days (well I'd love it to not). I guess the only other way to handle this is to use setFirstResult and setMaxResults to iterate through the results and just use regular Hibernate results instead of ScrollableResults. That feels like it will be inefficient though and will start taking a ridiculously long time when I'm calling setFirstResult on the 89 millionth row... UPDATE: setFirstResult/setMaxResults doesn't work, it turns out to take an unusably long time to get to the offsets like I feared. There must be a solution here! Isn't this a pretty standard procedure?? I'm willing to forgo Hibernate and use JDBC or whatever it takes. UPDATE 2: the solution I've come up with which works ok, not great, is basically of the form: select * from person where id > <offset> and <other_conditions> limit 1 Since I have other conditions, even all in an index, it's still not as fast as I'd like it to be... so still open for other suggestions..

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• Most efficient way of creating tree from adjacency list

  - by Jeff Meatball Yang

  I have an adjacency list of objects (rows loaded from SQL database with the key and it's parent key) that I need to use to build an unordered tree. It's guaranteed to not have cycles. This is taking wayyy too long (processed only ~3K out of 870K nodes in about 5 minutes). Running on my workstation Core 2 Duo with plenty of RAM. Any ideas on how to make this faster? public class StampHierarchy { private StampNode _root; private SortedList<int, StampNode> _keyNodeIndex; // takes a list of nodes and builds a tree // starting at _root private void BuildHierarchy(List<StampNode> nodes) { Stack<StampNode> processor = new Stack<StampNode>(); _keyNodeIndex = new SortedList<int, StampNode>(nodes.Count); // find the root _root = nodes.Find(n => n.Parent == 0); // find children... processor.Push(_root); while (processor.Count != 0) { StampNode current = processor.Pop(); // keep a direct link to the node via the key _keyNodeIndex.Add(current.Key, current); // add children current.Children.AddRange(nodes.Where(n => n.Parent == current.Key)); // queue the children foreach (StampNode child in current.Children) { processor.Push(child); nodes.Remove(child); // thought this might help the Where above } } } } public class StampNode { // properties: int Key, int Parent, string Name, List<StampNode> Children }

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• How should I handle persistence in a Java MUD? OptimisticLockException handling

  - by Chase

  I'm re-implementing a old BBS MUD game in Java with permission from the original developers. Currently I'm using Java EE 6 with EJB Session facades for the game logic and JPA for the persistence. A big reason I picked session beans is JTA. I'm more experienced with web apps in which if you get an OptimisticLockException you just catch it and tell the user their data is stale and they need to re-apply/re-submit. Responding with "try again" all the time in a multi-user game would make for a horrible experience. Given that I'd expect several people to be targeting a single monster during a fight I think the chance of an OptimisticLockException would be high. My view code, the part presenting a telnet CLI, is the EJB client. Should I be catching the PersistenceExceptions and TransactionRolledbackLocalExceptions and just retrying? How do you decide when to stop? Should I switch to pessimistic locking? Is persisting after every user command overkill? Should I be loading the entire world in RAM and dumping the state every couple of minutes? Do I make my session facade a EJB 3.1 singleton which would function as a choke point and therefore eliminating the need to do any type of JPA locking? EJB 3.1 singletons function as a multiple reader/single writer design (you annotate the methods as readers and writers). Basically, what is the best design and java persistence API for highly concurrent data changes in an application where it is not acceptable to present resubmit/retry prompts to the user?

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• Java and tomcat vs ASP.NET and IIS

  - by Mark Cooper

  Until recently I'd considered myself to be a pretty good web programmer (coming up for 10yrs commercial experience on a variety of e-commerce, static and enterprise applications). I'm self taught and have always used the Microsoft product stack (ASP, ASP.NET)... My applications are always functional, relatively bug free, but have never been lightening quick. As a frequent web user I always found this to be the norm... how fast are the websites from the big tech players (eBay, Facebook, Microsoft, IBM, Dell, Telerik etc etc) - in truth none are particularly fast. I always attributed this to "the way things are with web apps"... ...then I cam across a product called Jira from atlasian and this has stopped me in my tracks... This application is fast, and I mean blindingly fast.. too fast to time the switches between pages, fully live content, lots of images and data and cross references etc etc... I run this on an intranet, with a large application DB, and this is running on a very normal server (single processor, SATA HDD, 8GB RAM). Am I missing something?? Are my programming techniques that bad?? I am wondering if this speed gain is down to it being written in Java and running on Tomcat. Does anyone have any benchmarks to compare JSP / ASP or Tomcat / IIS??? Thanks, Mark NOTE: this isn't a blatant plug for Jira. I don't work for them or have any affiliation to them... but I would like to be able to write applications like them :)

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• Terrible DotNetNuke performance

  - by Peter Bridger

  I'm involved with a project using DotNetNuke version 05.01.04 Community Edition. We are building our new Intranet using it, but performance is terrible. We have five people adding pages and content to it and every 15-30 seconds they experience a pause of 10 seconds or longer before the system continues and the next screens loads. The server is Windows 2003, 3.8GHz with 1GB of RAM. I'm told by our server admin that the CPU and memory performance don't appear to be the bottleneck. We currently have 350 pages in the system, we a plan to add 1000. So we need to resolve this performance problem so that we can enter content and so we can go live. I just can't see where the bottleneck is. Is there a good why to determine the bottleneck when using DotNetNuke? Modules installed Publish:Engage (Not currently in use) Page Blaster (Doesn't appear to providing caching when users logged in using Integrated Authentication) SimpleGallery XMod Content Manager IIS Setup Application recycling completely disabled (Apart from a 2am recycle) New findings: 18th March 2010 The main bottleneck was due to version 5.1.4 having a bug which caused 1300 database roundtrips on an average page, due to broken database in-memory caching. We've upgraded to 5.2.4 which has resolved this bottleneck. Now the next biggest bottleneck is the navigation. We've used both DDR:Menu and DDN:Nav, but both have a major impact on performance. Is there a navigation interface out there that doesn't drain performance so badly?

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• Internet Explorer 8 timeout too quick on page POSTs

  - by cdm9002

  We have an asp.net site running, which has been working fine for some time, but recently I have been experiencing some issues with IE8. On posting some pages - mainly on our development server, although on staging too - we get an occasional "Internet Explore cannot display the webpage" error along with the button asking to diagnose connection problems. IE only seems to wait 10 seconds before timing out. I know that the page itself may take longer to load the first time (on dev and staging). So press F5 and everything then works fine. Is there anything that should be done in the aspx page to tell IE to wait a bit longer? I thought I had read that the default timeout supposed to be 90 seconds or something for browsers. A bit more info: It mostly happens on a POSTing a signup page, but that is just because I test that page and it starts the IIS App, makes the first connection to SQL and pre-caches some information. That first time the page can take 10-15 seconds to come back. IE8 times out after 10 seconds as it has had nothing back. This happens on a dev W7x64 machine with 8GB RAM, as well as on a staging server WIN2008. Having googled around a bit, some people are seeing the same problem, but no conclusive pointers to the problem or a solution. It isn't a connection problem; everything works fine in Firefox, Chrome and even IE7; I have tried with add-ons disabled and resetting IE settings, still happens. Ideas welcome.

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• How to setup matlabpool for multiple processors?

  - by JohnIdol

  I just setup a Extra Large Heavy Computation EC2 instance to throw it at my Genetic Algorithms problem, hoping to speed up things. This instance has 8 Intel Xeon processors (around 2.4Ghz each) and 7 Gigs of RAM. On my machine I have an Intel Core Duo, and matlab is able to work with my two cores just fine by runinng: matlabpool open 2 On the EC2 instance though, matlab only is capable of detecting 1 out of 8 processors, and if I try running: matlabpool open 8 I get an error saying that the ClusterSize is 1 since there's only 1 core on my CPU. True, there is only 1 core on each CPU, but I have 8 CPUs on the given EC2 instance! So the difference from my machine and the ec2 instance is that I have my 2 cores on a single processor locally, while the EC2 instance has 8 distinct processors. My question is, how do I get matlab to work with those 8 processors? I found this paper, but it seems related to setting up matlab with multiple EC2 instances (not related to multiple processors on the same instance, EC2 or not), which is not my problem. Any help appreciated!

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• Static Data Structures on Embedded Devices (Android in particular)

  - by Mark

  I've started working on some Android applications and have a question regarding how people normally deal with situations where you have a static data set and have an application where that data is needed in memory as one of the standard java collections or as an array. In my current specific issue i have a spreadsheet with some pre-calculated data. It consists of ~100 rows and 3 columns. 1 Column is a string, 1 column is a float, 1 column is an integer. I need access to this data as an array in java. It seems like i could: 1) Encode in XML - This would be cpu intensive to decode in my experience. 2) build into SQLite database - seems like a lot of overhead for static access to data i only need array style access to in ram. 3) Build into binary blob and read in. (never done this in java, i miss void *) 4) Build a python script to take the CSV version of my data and spit out a java function that adds the values to my desired structure with hard coded values. 5) Store a string array via androids resource mechanism and compute the other 2 columns on application load. In my case the computation would require a lot of calls to Math.log, Math.pow and Math.floor which i'd rather not have to do for load time and battery usage reasons. I mostly work in low power embedded applications in C and as such #4 is what i'm used to doing in these situations. It just seems like it should be far easier to gain access to static data structures in java/android. Perhaps I'm just being too battery usage conscious and in my single case i imagine the answer is that it doesn't matter much, but if every application took that stance it could begin to matter. What approaches do people usually take in this situation? Anything I missed?

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• MVC and repository pattern data effeciency

  - by Shawn Mclean

  My project is structured as follows: DAL public IQueryable<Post> GetPosts() { var posts = from p in context.Post select p; return posts; } Service public IList<Post> GetPosts() { var posts = repository.GetPosts().ToList(); return posts; } //Returns a list of the latest feeds, restricted by the count. public IList<PostFeed> GetPostFeeds(int latestCount) { List<Post> post - GetPosts(); //CODE TO CREATE FEEDS HERE return feeds; } Lets say the GetPostFeeds(5) is supposed to return the 5 latest feeds. By going up the list, doesn't it pull down every single post from the database from GetPosts(), just to extract 5 from it? If each post is say 5kb from the database, and there is 1 million records. Wont that be 5GB of ram being used per call to GetPostFeeds()? Is this the way it happens? Should I go back to my DAL and write queries that return only what I need?

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• Flash video slooow in AIR 2 HTMLLoader component

  - by shane

  I am working on a full screen kiosk application in Flex 4/Air 2 using Flash Builder 4. We have a company training website which staff can access via the kiosk, and the main content is interactive flash training videos. Our target machines are by no means 'beefy', they are Atom n270s @ 1.6Ghz with 1Gb RAM. As it stands the videos are all but unusable when used from within the Air application, the application becomes completely unresponsive (100% cpu usage, click events take approx 5-10 seconds to register). So far I have tried: increasing the default frame rate from 24fps to 60. No improvement. nativeWindow.stage.frameRate = 60; running the videos in a stripped down version of my app, just a full screen HTMLLoader component pointed at the training website. No better than before. disabled hyper threading. The Atom CPU is split into two virtual cores, and the AIR app was only able to use one thread so maxed out at 50% CPU usage. Since the kiosk will only run the AIR app I am happy to loose hyper threading to increase the performance of the Air app. Marginal Improvement. The same website with the same videos is responsive if viewed in ie7 on the same machine, although Internet Explorer takes advantage of the CPU’s hyper threading. The flash videos are built with Adobe Captivate and from what I understand employee JavaScript to relay results back to the server. I will add more information about the video content asap as the training guru is back in the office later this week.

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• Cloud-aware programming and help choosing a good framework

  - by Shoaibi

  How can i write a cloud-aware application? e.g. an application that takes benefit of being deployed on cloud. Is it same as an application that runs or a vps/dedicated server? if not then what are the differences? are there any design changes? What are the procedures that i need to take if i am to migrate an application to cloud-aware? Also i am about to implement a web application idea which would need features like security, performance, caching, and more importantly free. I have been comparing some frameworks and found that django has least RAM/CPU usage and works great in prefork+threaded mode, but i have also read that django based sites stop to respond with huge load of connections. Other frameworks that i have seen/know are Zend, CakePHP, Lithium/Cake3, CodeIgnitor, Symfony, Ruby on Rails.... So i would leave this to your opinion as well, suggest me a good free framework based on my needs. Finally thanks for reading the essay ;)

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• MVC and repository pattern data efficiency

  - by Shawn Mclean

  My project is structured as follows: DAL public IQueryable<Post> GetPosts() { var posts = from p in context.Post select p; return posts; } Service public IList<Post> GetPosts() { var posts = repository.GetPosts().ToList(); return posts; } //Returns a list of the latest feeds, restricted by the count. public IList<PostFeed> GetPostFeeds(int latestCount) { List<Post> post - GetPosts(); //CODE TO CREATE FEEDS HERE return feeds; } Lets say the GetPostFeeds(5) is supposed to return the 5 latest feeds. By going up the list, doesn't it pull down every single post from the database from GetPosts(), just to extract 5 from it? If each post is say 5kb from the database, and there is 1 million records. Wont that be 5GB of ram being used per call to GetPostFeeds()? Is this the way it happens? Should I go back to my DAL and write queries that return only what I need?

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• Debugging strategy to find the cause of bad_alloc

  - by SalamiArmi

  I have a fairly serious bug in my program - occasional calls to new() throw a bad_alloc. From the documentation I can find on bad_alloc, it seems to be thrown for these reasons: When the computer runs out of memory (which definitely isn't happening, I have 4GB of RAM, program throws bad_alloc when using less than 5MB (checked in taskmanager) with nothing serious running in the background). If the memory becomes too fragmented to allocate new blocks (which, again, is unlikely - the largest sized block I ever allocate would be about 1KB, and that doesn't get done more than 100 times before the crash occurs). Based on these descriptions, I don't really have anywhere in which a bad_alloc could be thrown. However, the application I am running runs more than one thread, which could possibly be contributing to the problem. By testing all of the objects on a single thread, everything seems to be working smoothly. The only other thing that I can think of that is going on here could be some kind of race-condition caused by calling new() in more than one place at the same time, but I've tried adding mutexes to prevent that behaviour to no effect. Because the program is several hundred lines and I have no idea where the problem actually lies, I'm not sure of what, if any, code snippets to post. Instead, I was wondering if there were any tools that will help me test for this kind of thing, or if there are any general strategies that can help me with this problem. I'm using Microsoft Visual Studio 2008, with Poco for threading.

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• Huge mysql table with Zend Framework

  - by Uffo

  I have a mysql table with over 4 million of data; well the problem is that SOME queries WORK and SOME DON'T it depends on the search term, if the search term has a big volume of data in the table than I get the following error: Fatal error: Allowed memory size of 1048576000 bytes exhausted (tried to allocate 75 bytes) in /home/****/public_html/Zend/Db/Statement/Pdo.php on line 290 I currently have Zend Framework cache for metadata enabled, I have index on all the fields from that table.The site is running on a dedicated server with 2gb of ram. I've also set memory limit to: ini_set("memory_limit","1000M"); Any other things that I can optimize? Those are the types of query that I'm currently using: $do = $this->select() ->where('branche LIKE ?','%'.mysql_escape_string($branche).'%') ->order('premium DESC'); } //For name if(empty($branche) && empty($plz)) { $do = $this->select("MATCH(`name`) AGAINST ('{$theString}') AS score") ->where('MATCH(`name`) AGAINST( ? IN BOOLEAN MODE)', $theString) ->order('premium DESC, score'); } And a few other, but they are pretty much the same. Best Regards

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• My OpenCL kernel is slower on faster hardware.. But why?

  - by matdumsa

  Hi folks, As I was finishing coding my project for a multicore programming class I came up upon something really weird I wanted to discuss with you. We were asked to create any program that would show significant improvement in being programmed for a multi-core platform. I’ve decided to try and code something on the GPU to try out OpenCL. I’ve chosen the matrix convolution problem since I’m quite familiar with it (I’ve parallelized it before with open_mpi with great speedup for large images). So here it is, I select a large GIF file (2.5 MB) [2816X2112] and I run the sequential version (original code) and I get an average of 15.3 seconds. I then run the new OpenCL version I just wrote on my MBP integrated GeForce 9400M and I get timings of 1.26s in average.. So far so good, it’s a speedup of 12X!! But now I go in my energy saver panel to turn on the “Graphic Performance Mode” That mode turns off the GeForce 9400M and turns on the Geforce 9600M GT my system has. Apple says this card is twice as fast as the integrated one. Guess what, my timing using the kick-ass graphic card are 3.2 seconds in average… My 9600M GT seems to be more than two times slower than the 9400M.. For those of you that are OpenCL inclined, I copy all data to remote buffers before starting, so the actual computation doesn’t require roundtrip to main ram. Also, I let OpenCL determine the optimal local-worksize as I’ve read they’ve done a pretty good implementation at figuring that parameter out.. Anyone has a clue? edit: full source code with makefiles here http://www.mathieusavard.info/convolution.zip cd gimage make cd ../clconvolute make put a large input.gif in clconvolute and run it to see results

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• Bare-metal virtualisation for the desktop

  - by Andrew Taylor

  Hi, Does anyone have any knowledge about bare-metal virtualisation products? I'm interested in building a new desktop machine for home, I've been looking at the Intel Quad Core processors and I'd like to put 8GB of RAM in there, but, it got me thinking about making the most out of the available resources. I thought if I could get a good 64bit machine, put some bare-metal virtualisation on, then have a primary system, I'd also be able to bring up some extra virtualised systems as and when I needed. I know most of the bare metal systems are designed for the server market, but, is there anything out there that works well for a desktop. What are the caveats? I presume I won't be able to make the most out of any video cards I could buy, what about just getting a decent screen resolution, will this be a problem? I run a single 24" screen. What about DVD/CD writing, is this possible? I'd like to re-rip my CD collection, I was hoping the quad 64Bit goodness would help me out with the encoding. I currently use a Mac and couldn't go back to windows so that leaves Linux, I was thinking a primary OS of ubuntu. Does this make a difference? Thanks Andrew

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• Cassandra random read speed

  - by Jody Powlette

  We're still evaluating Cassandra for our data store. As a very simple test, I inserted a value for 4 columns into the Keyspace1/Standard1 column family on my local machine amounting to about 100 bytes of data. Then I read it back as fast as I could by row key. I can read it back at 160,000/second. Great. Then I put in a million similar records all with keys in the form of X.Y where X in (1..10) and Y in (1..100,000) and I queried for a random record. Performance fell to 26,000 queries per second. This is still well above the number of queries we need to support (about 1,500/sec) Finally I put ten million records in from 1.1 up through 10.1000000 and randomly queried for one of the 10 million records. Performance is abysmal at 60 queries per second and my disk is thrashing around like crazy. I also verified that if I ask for a subset of the data, say the 1,000 records between 3,000,000 and 3,001,000, it returns slowly at first and then as they cache, it speeds right up to 20,000 queries per second and my disk stops going crazy. I've read all over that people are storing billions of records in Cassandra and fetching them at 5-6k per second, but I can't get anywhere near that with only 10mil records. Any idea what I'm doing wrong? Is there some setting I need to change from the defaults? I'm on an overclocked Core i7 box with 6gigs of ram so I don't think it's the machine. Here's my code to fetch records which I'm spawning into 8 threads to ask for one value from one column via row key: ColumnPath cp = new ColumnPath(); cp.Column_family = "Standard1"; cp.Column = utf8Encoding.GetBytes("site"); string key = (1+sRand.Next(9)) + "." + (1+sRand.Next(1000000)); ColumnOrSuperColumn logline = client.get("Keyspace1", key, cp, ConsistencyLevel.ONE); Thanks for any insights

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