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  • Tomcat startup logs - SEVERE: Error filterStart how to get a stack trace?

    - by Benju
    When I start Tomcat I get the following error: Jun 10, 2010 5:17:25 PM org.apache.catalina.core.StandardContext start SEVERE: Error filterStart Jun 10, 2010 5:17:25 PM org.apache.catalina.core.StandardContext start SEVERE: Context [/mywebapplication] startup failed due to previous errors It seems odd that the logs for Tomcat would not include a stack trace. Does somebody have a suggestion for how to increase the logging in Tomcat to get stack traces for errors like this?

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  • Java API to create pdf with tables: any recommendations?

    - by jack
    I need to create a PDF containing some tables. When looking on google/stackoverflow the most frequent API seems to be iText but that's under the AGPL licence and thus not desirable for my purposes. I also frequently see apache pdfbox but that does not seem to have native support for tables (although a slightly hacky way was posted at Apache PDFBox Java library - Is there an API for creating tables? ) Does anyone have any recommendations?

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  • mysql_connect randomly hangs up

    - by sergdev
    I install php 5 (more precisely 5.3.1) as apache module. After this one of my application becomes randomly hang up on mysql_connect - sometimes works, sometimes no, sometimes reload of page helps. How can this be fixed? I use Windows Vista, Apache/2.2.14 (Win32) PHP/5.3.1 with php module, MySql 5.0.67-community-nt.

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  • nginx bad gateway 502 with mono fastcgi

    - by Bradley Lederholz Leatherwood
    Hello so I have been trying to get my website to run on mono (on ubuntu server) and I have followed these tutorials almost to the letter: However when my directory is not blank fastcgi logs reveal this: Notice Beginning to receive records on connection. Error Failed to process connection. Reason: Exception has been thrown by the target of an invocation. I am not really sure what this means, and depending on what I do I can get another error that tells me the resource cannot be found: The resource cannot be found. Description: HTTP 404. The resource you are looking for (or one of its dependencies) could have been removed, had its name changed, or is temporarily unavailable. Please review the following URL and make sure that it is spelled correctly. Requested URL: /Default.aspx/ Version information: Mono Runtime Version: 2.10.8 (tarball Thu Aug 16 23:46:03 UTC 2012) ASP.NET Version: 4.0.30319.1 If I should provide some more information please let me know. Edit: I am now getting a nginx gateway error. My nginx configuration file looks like this: server { listen 2194; server_name localhost; access_log $HOME/WWW/nginx.log; location / { root $HOME/WWW/dev/; index index.html index.html default.aspx Default.aspx Index.cshtml; fastcgi_index Views/Home/; fastcgi_pass 127.0.0.1:8000; include /etc/nginx/fastcgi_params; } } Running the entire thing with xsp4 I have discovered what the "Exception has been thrown by the target of an invocation." Handling exception type TargetInvocationException Message is Exception has been thrown by the target of an invocation. IsTerminating is set to True System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. Server stack trace: at System.Reflection.MonoCMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in :0 at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in :0 at System.Runtime.Serialization.ObjectRecord.LoadData (System.Runtime.Serialization.ObjectManager manager, ISurrogateSelector selector, StreamingContext context) [0x00000] in :0 at System.Runtime.Serialization.ObjectManager.DoFixups () [0x00000] in :0 at System.Runtime.Serialization.Formatters.Binary.ObjectReader.ReadNextObject (System.IO.BinaryReader reader) [0x00000] in :0 at System.Runtime.Serialization.Formatters.Binary.ObjectReader.ReadObjectGraph (BinaryElement elem, System.IO.BinaryReader reader, Boolean readHeaders, System.Object& result, System.Runtime.Remoting.Messaging.Header[]& headers) [0x00000] in :0 at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.NoCheckDeserialize (System.IO.Stream serializationStream, System.Runtime.Remoting.Messaging.HeaderHandler handler) [0x00000] in :0 at System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Deserialize (System.IO.Stream serializationStream) [0x00000] in :0 at System.Runtime.Remoting.RemotingServices.DeserializeCallData (System.Byte[] array) [0x00000] in :0 at (wrapper xdomain-dispatch) System.AppDomain:DoCallBack (object,byte[]&,byte[]&) Exception rethrown at [0]: --- System.ArgumentException: Couldn't bind to method 'SetHostingEnvironment'. at System.Delegate.GetCandidateMethod (System.Type type, System.Type target, System.String method, BindingFlags bflags, Boolean ignoreCase, Boolean throwOnBindFailure) [0x00000] in :0 at System.Delegate.CreateDelegate (System.Type type, System.Type target, System.String method, Boolean ignoreCase, Boolean throwOnBindFailure) [0x00000] in :0 at System.Delegate.CreateDelegate (System.Type type, System.Type target, System.String method) [0x00000] in :0 at System.DelegateSerializationHolder+DelegateEntry.DeserializeDelegate (System.Runtime.Serialization.SerializationInfo info) [0x00000] in :0 at System.DelegateSerializationHolder..ctor (System.Runtime.Serialization.SerializationInfo info, StreamingContext ctx) [0x00000] in :0 at (wrapper managed-to-native) System.Reflection.MonoCMethod:InternalInvoke (System.Reflection.MonoCMethod,object,object[],System.Exception&) at System.Reflection.MonoCMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in :0 --- End of inner exception stack trace --- at (wrapper xdomain-invoke) System.AppDomain:DoCallBack (System.CrossAppDomainDelegate) at (wrapper remoting-invoke-with-check) System.AppDomain:DoCallBack (System.CrossAppDomainDelegate) at System.Web.Hosting.ApplicationHost.CreateApplicationHost (System.Type hostType, System.String virtualDir, System.String physicalDir) [0x00000] in :0 at Mono.WebServer.VPathToHost.CreateHost (Mono.WebServer.ApplicationServer server, Mono.WebServer.WebSource webSource) [0x00000] in :0 at Mono.WebServer.XSP.Server.RealMain (System.String[] args, Boolean root, IApplicationHost ext_apphost, Boolean quiet) [0x00000] in :0 at Mono.WebServer.XSP.Server.Main (System.String[] args) [0x00000] in :0

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  • Compilation of Etherpad fails in an OpenVZ VE

    - by ulf
    Hi everyone. I’m almost giving up, this will be my last try: I try to compile Etherpad on my OpenVZ server. It’s running a Debian 5.0 as the host system, in the VE I’ve got Ubuntu 10.04. I installed Etherpad in this VE with the instructions from the official Ubuntu Wiki: https://wiki.ubuntu.com/Etherpad. Everything runs fine until it comes to compilation. After calling bin/build.sh as described in the wiki the first steps are running fine. But then I’m running into a memory error: java.io.IOException: Cannot run program "cp": java.io.IOException: error=12, Cannot allocate memory Well, I understand the error message but don’t see the cause. The command free tells me that there’s plenty memory left in this VE: total used free shared buffers cached Mem: 2415236 1140872 1274364 0 0 0 -/+ buffers/cache: 1140872 1274364 Swap: 0 0 0 Beautiful. But even repeating the compilation process doesn’t bring me any further. Any help would be appreciated.

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  • perl : Passing hash , array through socket program betwen client and server

    - by pavun_cool
    Hi All . In sockets I have written the client server program . First I tried to send the normal string among them it sends fine . After that I am trying to send the hash and array values from client to server and server to client . When I printing the values using Dumper . It is giving me only reference . What Should I do for getting accessing the actual values in client server . Server Program: use IO::Socket; use strict; use warnings; my %hash = ( "name" => "pavunkumar " , "age" => 20 ) ; my $new = \%hash ; #Turn on System variable for Buffering output $| = 1; # Creating a a new socket my $socket= IO::Socket::INET->new(LocalPort=>5000,Proto=>'tcp',Localhost => 'localhost','Listen' => 5 , 'Reuse' => 1 ); die "could not create $! \n" unless ( $socket ); print "\nUDPServer Waiting port 5000\n"; my $new_sock = $socket->accept(); my $host = $new_sock->peerhost(); while(<$new_sock>) { #my $line = <$new_sock>; print Dumper "$host $_"; print $new_sock $new . "\n"; } print "$host is closed \n" ; Client Program use IO::Socket; use Data::Dumper ; use warnings ; use strict ; my %hash = ( "file" =>"log.txt" , size => "1000kb") ; my $ref = \%hash ; # This client for connecting the specified below address and port # INET function will create the socket file and establish the connection with # server my $port = shift || 5000 ; my $host = shift || 'localhost'; my $recv_data ; my $send_data; my $socket = new IO::Socket::INET ( PeerAddr => $host , PeerPort => $port , Proto => 'tcp', ) or die "Couldn't connect to Server\n"; while (1) { my $line = <stdin> ; print $socket $ref."\n"; if ( $line = <$socket> ) { print Dumper $line ; } else { print "Server is closed \n"; last ; } } I have given my sample program about what I am doing , Can any one tell me what I am doing wrong in this code. And what I need to do for accessing the hash values . Thanks in Advance

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  • Can't get java progam to run! NoClassDefFoundError?

    - by mcintyre321
    I'm a .NET developer, but for my current project I need to use Google Caja, a Java project. Uh-oh! I've followed the guide at http://code.google.com/p/google-caja/wiki/RunningCaja on my windows machine, but can't get the program to run. The command line they suggest didn't word, so I cd'd into the ant-jars directory and tried to run plugin.jar: D:\java\caja\svn-changes\pristine\ant-jars>java -cp . -jar pluginc.jar -i test.htm Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/cli/ParseException at com.google.caja.plugin.PluginCompilerMain.<init>(PluginCompilerMain.java:78) at com.google.caja.plugin.PluginCompilerMain.main(PluginCompilerMain.java:368) Caused by: java.lang.ClassNotFoundException: org.apache.commons.cli.ParseException at java.net.URLClassLoader$1.run(URLClassLoader.java:202) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:248) ... 2 more Whats that all about? I've also tried file:///d:/java/caja/svn-changes/pristine/ant-jars/test.htm instead of test.htm as looking at the source it seems the file param is a Uri... I've also tried running IKVM on pluginc and then not worrying about java, but that came up with the ClassDefNotFoundException too... thanks!

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  • Tapestry5 : No service implements the interface org.springframework.context.ApplicationContext

    - by Joel
    I'm using the Tapestry5 tapx template library to send an html email, as per this example. When I run the example I get the following error: Caused by: java.lang.RuntimeException: No service implements the interface org.springframework.context.ApplicationContext. at org.apache.tapestry5.ioc.internal.RegistryImpl.getService(RegistryImpl.java:560) at org.apache.tapestry5.ioc.internal.ObjectLocatorImpl.getService(ObjectLocatorImpl.java:44) All the tapestry-* jars, including tapestry-spring-5.1.05.jar are in my classpath. Any clues as to what I'm missing?

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  • What does directory permission 'S' mean? (not lower case, but in upper case)

    - by Howard Guo
    I downloaded Eclipse, uncompressed it, did a few other things and all sudden I notice this interesting behaviour: ^_^ ~/Downloads > sudo chmod 0000 eclipse/ ^_^ ~/Downloads > stat eclipse/ File: 'eclipse/' Size: 4096 Blocks: 8 IO Block: 4096 directory Device: 801h/2049d Inode: 529725 Links: 9 Access: (2000/d-----S---) Uid: ( 0/ root) Gid: ( 0/ root) Access: 2012-11-22 19:54:57.752017352 +1100 Modify: 2012-09-20 18:16:26.000000000 +1000 Change: 2012-11-22 20:07:49.354016510 +1100 Birth: - ^_^ ~/Downloads > sudo chmod 0755 eclipse/ ^_^ ~/Downloads > stat eclipse/ File: 'eclipse/' Size: 4096 Blocks: 8 IO Block: 4096 directory Device: 801h/2049d Inode: 529725 Links: 9 Access: (2755/drwxr-sr-x) Uid: ( 0/ root) Gid: ( 0/ root) Access: 2012-11-22 19:54:57.752017352 +1100 Modify: 2012-09-20 18:16:26.000000000 +1000 Change: 2012-11-22 20:08:19.042016478 +1100 Birth: - What does 'S' permission mean to a directory? And why it doesn't let me get rid of it? Thanks.

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  • Unable to start Tomcat 6.x when Mac OS X 10.6 is boot up

    - by SkyEagle888
    I am using Mac OS X 10.6 and installed MAMP and Tomcat. My Tomcat is installed in /Users/(userID)/Tomcat I can start Tomcat server in Terminal without a problem But it cannot be started automatically when Mac OS X is boot up. I put a file org.apache.tomcat.plist in /Library/LaunchDaemons Disabled Label org.apache.tomcat ProgramArguments /Users/henryfok/Tomcat/bin/startup.sh RunAtLoad Any hint ?

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  • Tomcat does not persist Session during restart

    - by mabuzer
    How to force Tomcat to serialize Session so that the user is kept logged in when Tomcat has restarted? Right now the user has to login again everytime. Added the following lines into web-app context.xml: <Manager className="org.apache.catalina.session.PersistentManager"> <Store className="org.apache.catalina.session.FileStore"/> </Manager> but still I see login page after Tomcat restart, I use Tomcat 6.0.24

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  • Sending XML to Servlet from Action Script

    - by John Doe
    I am only getting empty arrays on output. Anyone know what Exactly I'm doing wrong? package myDungeonAccessor; /* * To change this template, choose Tools | Templates * and open the template in the editor. */ import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class myDungeonAccessorServlet extends HttpServlet { private myDungeonAccessor dataAccessor; /** * Processes requests for both HTTP <code>GET</code> and <code>POST</code> methods. * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); try { /* TODO output your page here out.println("<html>"); out.println("<head>"); out.println("<title>Servlet myDungeonAccessorServlet</title>"); out.println("</head>"); out.println("<body>"); out.println("<h1>Servlet myDungeonAccessorServlet at " + request.getContextPath () + "</h1>"); out.println("</body>"); out.println("</html>"); */ } finally { out.close(); } } // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code."> /** * Handles the HTTP <code>GET</code> method. * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { processRequest(request, response); // PrintWriter out = response.getWriter(); System.out.println("yo mom"); } /** * Handles the HTTP <code>POST</code> method. * @param request servlet request * @param response servlet response * @throws ServletException if a servlet-specific error occurs * @throws IOException if an I/O error occurs */ @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //System.out.println("heppo"); //dataAccessor = new myDungeonAccessor(); System.out.println("Hello"); try { System.out.println("HEADERS: " + request.getHeaderNames()); ObjectInputStream in = new ObjectInputStream(request.getInputStream()); ObjectOutputStream out = new ObjectOutputStream(response.getOutputStream()); } catch(Exception e) { e.printStackTrace(); } System.out.println("WAZZUP"); byte [] buffer = new byte[4096]; //in.read(buffer); System.out.println("TEST!"); String s = new String(buffer); System.out.println("Update S:" + s); } /** * Returns a short description of the servlet. * @return a String containing servlet description */ @Override public String getServletInfo() { return "Short description"; } }

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  • SharePoint List Service Recursive not working

    - by stranger001
    Hi, I am using the following code to retrieve the documents in a list. Its working fine. However, it only returns documents and folders in root of the doc library. Is there any thing wrong I am doing here? I am looking for files in sub folders with recursive mode. Service service = new Service(); service.setMaintainSession(true); call = (Call) service.createCall(); call.setTargetEndpointAddress( new java.net.URL("<host>/_vti_bin/lists.asmx") ); call.setOperationName(new QName("http://schemas.microsoft.com/sharepoint/soap/","GetListItems")); call.setProperty(Call.SOAPACTION_USE_PROPERTY, new Boolean("true")); call.setProperty(Call.SOAPACTION_URI_PROPERTY,"http://schemas.microsoft.com/sharepoint/soap/GetListItems"); call.addParameter(new javax.xml.namespace.QName("http://schemas.microsoft.com/sharepoint/soap/", "listName"), new javax.xml.namespace.QName("http://www.w3.org/2001/XMLSchema", "string"), java.lang.String.class, javax.xml.rpc.ParameterMode.IN); MessageElement me = new MessageElement(new QName("QueryOptions")); me.addChildElement(new MessageElement(new QName( "IncludeMandatoryColumns"))).addTextNode("true"); me.addChildElement(new MessageElement(new QName( "ViewAttributes"))).addAttribute(javax.xml.soap.SOAPFactory.newInstance().createName("Scope"), "Recursive"); MessageElement[] me1 = {me}; String strMyString = "" + "<Query>" + "<OrderBy><FieldRef Name=\"ows_Modified\" Ascending=\"TRUE\" /></OrderBy>" + "</Query>"; MessageElement[] meArray = { getMeFromString(strMyString) };// Array call.addParameter("query",org.apache.axis.Constants.XSD_SCHEMA, javax.xml.rpc.ParameterMode.IN); call.addParameter("queryOptions",org.apache.axis.Constants.XSD_SCHEMA, javax.xml.rpc.ParameterMode.IN); call.setReturnType(org.apache.axis.Constants.XSD_SCHEMA); Schema ret = (Schema)call.invoke(new Object[] {"listGUID",meArray, me1 }); public org.apache.axis.message.MessageElement getMeFromString(final String strMyString) { DocumentBuilder docBuilder = null; try { docBuilder = DocumentBuilderFactory.newInstance().newDocumentBuilder(); } catch (final ParserConfigurationException e) { e.printStackTrace(); } catch (final FactoryConfigurationError e) { e.printStackTrace(); } final StringReader reader = new StringReader(strMyString); final InputSource inputsource = new InputSource(reader); Document doc = null; try { doc = docBuilder.parse(inputsource); } catch (final SAXException e) { e.printStackTrace(); } catch (final IOException e) { e.printStackTrace(); } final Element ele = doc.getDocumentElement(); final MessageElement msg = new MessageElement(ele); return msg; }

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  • JBoss admin-console fails to load - missing Log4J jar?

    - by Jack
    I downloaded JBoss 5.1 and unzipped to ~/jboss/ such that JBoss is installed into: ~/jboss/jboss-5.1.0.GA/ I run the default deployment by using the following command found in jboss/jboss-5.1.0.GA/bin ./run.sh -c default While JBoss starts (http://127.0.0.1:8080/), admin-console is not deployed. The log file: jboss/jboss-5.1.0.GA/server/default/log shows the following information: DEPLOYMENTS IN ERROR: Deployment "vfsfile:/Users/jackwootton/jboss/jboss-5.1.0.GA/server/default/deploy/admin-console.war/" is in error due to the following reason(s): org.jboss.deployers.spi.DeploymentException: URL file:/Users/jackwootton/jboss/jboss-5.1.0.GA/server/default/tmp/az6n6v-tjilfb-h32fokxn-1-h32fosuo-v/admin-console.war/ deployment failed Deployment "vfszip:/Users/jackwootton/jboss/jboss-5.1.0.GA/server/default/deploy/quartz-ra.rar/" is in error due to the following reason(s): org.apache.commons.logging.LogConfigurationException: User-specified log class 'org.apache.commons.logging.impl.Log4JLogger' cannot be found or is not useable. The Log4J jar file exists in: jboss/jboss-5.1.0.GA/lib/jboss-logging-log4j.jar I have three questions: Have I understood the problem correctly (i.e. that admin-console cannot find the required Log4j JAR file and therefore is not deployed)? What can I do to fix this problem? Why would an out-of-the-box deployment have this problem in the first place?

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  • Tomcat does not persist UserPrinciple during restart

    - by mabuzer
    How to force Tomcat to serialize UserPrinciple so that the user is kept logged in when Tomcat has restarted? Right now the user has to login again everytime. Added the following lines into web-app context.xml: <Manager className="org.apache.catalina.session.PersistentManager"> <Store className="org.apache.catalina.session.FileStore"/> </Manager> but still I see login page after Tomcat restart, I use Tomcat 6.0.26

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  • Turn off write barriers on ext4 whiche FS is mounted

    - by user462982
    I am doing some IO intensive DB imports that run for several days now and the IO performance has dropped tremendously over times. The DB data files (log files) are on an ext4 formatted logical volume which is mounted with default options (did not specify something special in fstab). Since I just learned that ext4 enables write barriers by default: Q: Is there some way to disable write barriers online (i.e. while the file system is in use), because I cannot interrupt the import and don't want to restart it again. I am aware that write barriers might not be the only thing impeding performance it is a bad idea to have write barriers disabled on journalling file systems if data safty is important (e.g. on a production system)

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  • ionice idle is ignored

    - by Ferran Basora
    I have been testing the ionice command for a while and the idle (3) mode seems to be ignored in most cases. My test is to run both command at the same time: du <big folder> ionice -c 3 du <another big folder> If I check both process in iotop I see no difference in the percentage of io utilization for each process. To provide more information about the CFQ scheduler I'm using a 3.5.0 linux kernel. I started doing this test because I'm experimenting a system lag each time a daily cron job updatedb.mlocate is executed in my Ubuntu 12.10 machine. If you check the /etc/cron.daily/mlocate file you realize that the command is executed like: /usr/bin/ionice -c3 /usr/bin/updatedb.mlocate Also, the funny thing is that whenever my system for some reason starts using swap memory, the updatedb.mlocate io process is been scheduled faster than kswapd0 process, and then my system gets stuck. Some suggestion? References: http://ubuntuforums.org/showthread.php?t=1243951&page=2 https://bugs.launchpad.net/ubuntu/+source/findutils/+bug/332790

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  • MySQL keeps crashing due to bug

    - by mike
    So about a week ago, I finally figured out what was causing my server to continually crash. After reviewing my mysqld.log I keep seeing this same error, 101210 5:04:32 [Warning] option 'max_join_size': unsigned value 18446744073709551615 adjusted to 4294967295 Here is a link to the bug report, http://bugs.mysql.com/bug.php?id=35346 someone recommend that you set the max_join_size vaule in my.cnf to 4M, and I did. I assumed this fixed the issue, and it was working for about a week with no issues until today... I checked MySQL and the same error is now back, 101216 06:35:25 mysqld restarted 101216 6:38:15 [Warning] option 'max_join_size': unsigned value 18446744073709551615 adjusted to 4294967295 101216 6:38:15 [Warning] option 'max_join_size': unsigned value 18446744073709551615 adjusted to 4294967295 101216 06:40:42 mysqld ended Anyone know how I can really fix this issue? I can't keep having mysql crash like this. EDIT: I forgot to mention every time this happens I get an email from linode staying I have a high disk io rate Your Linode, has exceeded the notification threshold (1000) for disk io rate by averaging 2483.68 for the last 2 hours.

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  • Haskell: monadic takeWhile?

    - by Mark Rushakoff
    I have some functions written in C that I call from Haskell. These functions return IO (CInt). Sometimes I want to run all of the functions regardless of what any of them return, and this is easy. For sake of example code, this is the general idea of what's happening currently: Prelude> let f x = print x >> return x Prelude> mapM_ f [0..5] 0 1 2 3 4 5 Prelude> I get my desired side effects, and I don't care about the results. But now I need to stop execution immediately after the first item that doesn't return my desired result. Let's say a return value of 4 or higher requires execution to stop - then what I want to do is this: Prelude> takeWhile (<4) $ mapM f [0..5] Which gives me this error: <interactive:1:22: Couldn't match expected type `[b]' against inferred type `IO a' In the first argument of `mapM', namely `f' In the second argument of `($)', namely `mapM f ([0 .. 5])' In the expression: takeWhile (< 4) $ mapM f ([0 .. 5]) And that makes sense to me - the result is still contained in the IO monad, and I can't just compare two values contained in the IO monad. I know this is precisely the purpose of monads -- chaining results together and discarding operations when a certain condition is met -- but is there an easy way to "wrap up" the IO monad in this case to stop executing the chain upon a condition of my choosing, without writing an instance of MonadPlus? Can I just "unlift" the values from f, for the purposes of the takeWhile? Is this a solution where functors fit? Functors haven't "clicked" with me yet, but I sort of have the impression that this might be a good situation to use them. Update: @sth has the closest answer to what I want - in fact, that's almost exactly what I was going for, but I'd still like to see whether there is a standard solution that isn't explicitly recursive -- this is Haskell, after all! Looking back on how I worded my question, now I can see that I wasn't clear enough about my desired behavior. The f function I used above for an example was merely an example. The real functions are written in C and used exclusively for their side effects. I can't use @Tom's suggestion of mapM_ f (takeWhile (&lt;4) [0..5]) because I have no idea whether any input will really result in success or failure until executed. I don't actually care about the returned list, either -- I just want to call the C functions until either the list is exhausted or the first C function returns a failure code. In C-style pseudocode, my behavior would be: do { result = function_with_side_effects(input_list[index++]); } while (result == success && index < max_index); So again, @sth's answer performs the exact behavior that I want, except that the results may (should?) be discarded. A dropWhileM_ function would be equivalent for my purposes. Why isn't there a function like that or takeWhileM_ in Control.Monad? I see that there was a similar discussion on a mailing list, but it appears that nothing has come of that.

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  • MySQL connection timeout

    - by NikolayGS
    I'm running program at apache tomcat server, that should be on permanently, but every morning(the client part isn't accessible at night) i receive error message (in apache tomcat console) that MySQL server is off. So is there any way to prevent this? Thanks in advance!

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  • Only Execute Code on Certain Requests Java

    - by BillPull
    I am building a little API for class and the teacher supplied us with a link to a tutorial that provided a simple webserver that implements Runnable. I have already written some code that will parse arguments the arguments ( or at least get me the request string ) and some code that will return some simple xml. however I think certain requests like the one for the favicon are sent I think it is messing up my code. I wrapped that in an if else but it does not seem to be working. package server; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.net.Socket; import java.util.*; import java.io.*; import java.net.*; import parkinglots.*; public class WorkerRunnable implements Runnable{ protected Socket clientSocket = null; protected String serverText = null; public WorkerRunnable(Socket clientSocket, String serverText) { this.clientSocket = clientSocket; this.serverText = serverText; } public Boolean authenticateAPI(String key){ //Authenticate Key against Stored Keys //TODO: Create Stored Keys and Compare return true; } public void run() { try { InputStream input = clientSocket.getInputStream(); OutputStream output = clientSocket.getOutputStream(); long time = System.currentTimeMillis(); //TODO: Parse args and output different formats and Authentication //Parse URL Arguments BufferedReader in = new BufferedReader( new InputStreamReader(clientSocket.getInputStream(), "8859_1")); String request = in.readLine(); //Server gets Favicon Request so skip that and goto args System.out.println(request); if ( request != "GET /favicon.ico HTTP/1.1" && request != "GET / HTTP/1.1" && request != null ){ String format = "", apikey =""; System.out.println("I am Here"); String request_location = request.split(" ")[1]; String request_args = request_location.replace("/",""); request_args = request_args.replace("?",""); String[] queries = request_args.split("&"); System.out.println(queries[0]); for ( int i = 0; i < queries.length; i++ ){ if( queries[i] == "format" ){ format = queries[i].split("=")[1]; } else if( queries[i] == "apikey" ){ apikey = queries[i].split("=")[1]; } } if( apikey == "" ){ apikey = "None"; } if( format == "" ){ format = "xml"; } Boolean auth = authenticateAPI(apikey); if ( auth ){ if ( format == "xml"){ // Retrieve XML Document String xml = LotFromDB.getParkingLotXML(); output.write((xml).getBytes()); }else{ //Retrieve JSON String json = LotFromDB.getParkingLotJSON(); output.write((json).getBytes()); } }else{ output.write(("Access Denied - User is Not Authenticated").getBytes()); } }else{ output.write(("Access Denied Must Pass API Key").getBytes()); } output.close(); input.close(); System.out.println("Request processed: " + time); } catch (IOException e) { //report exceptions e.printStackTrace(); } } } Console output I get I am Here format=json Request processed: 1333516648331 GET /favicon.ico HTTP/1.1 I am Here favicon.ico Request processed: 1333516648332 It always returns the XML as well. This is my first exposure to writing a web server and dealing with networking in Java, which frustrates me a lot in general, So any suggestions here are very appreciated.

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