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• Need help with regular expressions - URL redirection

  - by paperless

  Hello everyone. I'm trying to redirect an easy to remember url to a php file but I'm having some trouble with the regex. Here's what I have at the moment: RewriteRule ^tcb/([a-zA-Z0-9]{1,})/([a-zA-Z0-9]{1,})/([a-zA-Z0-9]{1,}) /tcb/lerbd.php?autocarro=$1&tipo=$2&dsd=$3 It is working but only if I supply all 3 arguments. I want the last two arguments to be optional so it either works with only the first or all three. I'm hoping you can help me with this. Thank you very much.

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• python-like Java IO library?

  - by drozzy

  Java is not my main programming language so I might be asking the obvious. But is there a simple file-handling library in Java, like in python? For example I just want to say: File f = Open('file.txt', 'w') for(String line:f){ //do something with the line from file } Thanks!

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• SQL Server Redirection

  - by MrTehee

  We are switching from a SQL cluster to a mirrored solution. The problem is that we have a bunch of programs that would have to switch connection strings to handle the failover. Is there any way the we can set up a redirect or proxy that would take any legacy requests and forward them to the mirrored solution?

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• Using reflection to change static final File.separatorChar for unit testing?

  - by Stefan Kendall

  Specifically, I'm trying to create a unit test for a method which requires uses File.separatorChar to build paths on windows and unix. The code must run on both platforms, and yet I get errors with JUnit when I attempt to change this static final field. Anyone have any idea what's going on? Field field = java.io.File.class.getDeclaredField( "separatorChar" ); field.setAccessible(true); field.setChar(java.io.File.class,'/'); When I do this, I get IllegalAccessException: Can not set static final char field java.io.File.separatorChar to java.lang.Character Thoughts?

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• Problem with do construct in haskell

  - by Anonymous Coward

  Hello everyone I'm trying to learn Haskell and want to write a small program which prints the content of a file to the screen. When I load it into GHCi I get the following error: The last statement in a 'do' construct must be an expression I know this question has be asked already here: Haskell — “The last statement in a 'do' construct must be an expression”. Even though my code is very similar I still can't figure out the problem. If anyone could point out the problem to me I'd be very thankful. module Main (main) where import System.IO import System(getArgs) main :: IO() main = do args <- getArgs inh <- openFile $ ReadMode head args printFile inh hClose inh printFile :: Handle -> IO () printFile handle = do end <- hIsEOF handle if end then return () else do line <- hGetLine handle putStrLn line printFile handle

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• Event on SQL Server 2008 Disk IO and the new Complex Event Processing (StreamInsight) feature in R2

  - by tonyrogerson

  Allan Mitchell and myself are doing a double act, Allan is becoming one of the leading guys in the UK on StreamInsight and will give an introduction to this new exciting technology; on top of that I'll being talking about SQL Server Disk IO - well, "Disk" might not be relevant anymore because I'll be talking about SSD and IOFusion - basically I'll be talking about the underpinnings - making sure you understand and get it right, how to monitor etc... If you've any specific problems or questions just ping me an email [email protected]. To register for the event see: http://sqlserverfaq.com/events/217/SQL-Server-and-Disk-IO-File-GroupsFiles-SSDs-FusionIO-InRAM-DBs-Fragmentation-Tony-Rogerson-Complex-Event-Processing-Allan-Mitchell.aspx 18:15 SQL Server and Disk IOTony Rogerson, SQL Server MVPTony's Blog; Tony on TwitterIn this session Tony will talk about RAID levels, how SQL server writes to and reads from disk, the effect SSD has and will talk about other options for throughput enhancement like Fusion IO. He will look at the effect fragmentation has and how to minimise the impact, he will look at the File structure of a database and talk about what benefits multiple files and file groups bring. We will also touch on Database Mirroring and the effect that has on throughput, how to get a feeling for the throughput you should expect.19:15 Break19:45 Complex Event Processing (CEP)Allan Mitchell, SQL Server MVPhttp://sqlis.com/sqlisStreamInsight is Microsoft’s first foray into the world of Complex Event Processing (CEP) and Event Stream Processing (ESP).  In this session I want to show an introduction to this technology.  I will show how and why it is useful.  I will get us used to some new terminology but best of all I will show just how easy it is to start building your first CEP/ESP application.

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• VMWare Esxi Looking for Bottlenecks

  - by nextgenneo

  I have a VMWare ESxi box, 22GB ram, Dual Quad Core Xeon, 2 Sas drives + Write caching raid controller etc. Anyways, have about 30 small XP VM's running on it and starting to get some very slow boot times and other performance issues. I THINK its I/O but looking at the graphs not too sure what to look for. Any ideas on what to look for would be appreciated. Here is the data I've got so far: (I feel like my IO is high but not sure what to bench it against)

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• Design to distribute work when generating task oriented input for legacy dos application?

  - by TheDeeno

  I'm attempting to automate a really old dos application. I've decided the best way to do this is via input redirection. The legacy app (menu driven) has many tasks within tasks with branching logic. In order to easily understand and reuse the input for these tasks, I'd like to break them into bit size pieces. Since I'll need to start a fresh app on each run, repeating a context to consume a bit might be messy. I'd like to create an object model that: allows me to concentrate on the task at hand allows me to reuse common tasks from different start points prevents me from calling a task from the wrong start point To be more explicit, given I have the following task hierarchy: START A A1 A1a A1b A2 A2a B B1 B1a I'd like an object model that lets me generate an input file for task "A1b" buy using building blocks like: START -> do_A, do_A1, do_A1b but prevents me from: START -> do_A1 // because I'm assuming a different call chain from above This will help me write "do_A1b" because I can always assume the same starting context and will simplify writing "do_A1a" because it has THE SAME starting context. What patterns will help me out here? I'm using ruby at the moment so if dynamic language features can help, I'm game.

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• Is the XP VMM a bottleneck on a multi core machine?

  - by JeffV

  I have a dual Xeon hex core machine running an IO intensive application. (WinXP 32) I am seeing a hardware driver (1/2 user mode, 1/2 kernel, streaming data) that is using 6k delta page faults per second. When other applications load or allocate large amounts of memory the driver's hardware buffer gets an underrun (application not feeding it fast enough). Could this be because the kernel is only using one core to service page fault interrupts?

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• VS2008: File creation fails randomly in unit testing?

  - by Tim

  I'm working on implementing a reasonably simple XML serializer/deserializer (log file parser) application in C# .NET with VS 2008. I have about 50 unit tests right now for various parts of the code (mostly for the various serialization operations), and some of them seem to be failing mostly at random when they deal with file I/O. The way the tests are structured is that in the test setup method, I create a new empty file at a certain predetermined location, and close the stream I get back. Then I run some basic tests on the file (varying by what exactly is under test). In the cleanup method, I delete the file again. A large portion (usually 30 or more, though the number varies run to run) of my unit tests will fail at the initialize method, claiming they can't access the file I'm trying to create. I can't pin down the exact reason, since a test that will work one run fails the next; they all succeed when run individually. What's the problem here? Why can't I access this file across multiple unit tests? Relevant methods for a unit test that will fail some of the time: [TestInitialize()] public void LogFileTestInitialize() { this.testFolder = System.Environment.GetFolderPath( System.Environment.SpecialFolder.LocalApplicationData ); this.testPath = this.testFolder + "\\empty.lfp"; System.IO.File.Create(this.testPath); } [TestMethod()] public void LogFileConstructorTest() { string filePath = this.testPath; LogFile target = new LogFile(filePath); Assert.AreNotEqual(null, target); Assert.AreEqual(this.testPath, target.filePath); Assert.AreEqual("empty.lfp", target.fileName); Assert.AreEqual(this.testFolder + "\\empty.lfp.lfpdat", target.metaPath); } [TestCleanup()] public void LogFileTestCleanup() { System.IO.File.Delete(this.testPath); } And the LogFile() constructor: public LogFile(String filePath) { this.entries = new List<Entry>(); this.filePath = filePath; this.metaPath = filePath + ".lfpdat"; this.fileName = filePath.Substring(filePath.LastIndexOf("\\") + 1); } The precise error message: Initialization method LogFileParserTester.LogFileTest.LogFileTestInitialize threw exception. System.IO.IOException: System.IO.IOException: The process cannot access the file 'C:\Users\<user>\AppData\Local\empty.lfp' because it is being used by another process..

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• Sending multiline message via sockets without closing the connection

  - by Yasir Arsanukaev

  Hello folks. Currently I have this code of my client-side Haskell application: import Network.Socket import Network.BSD import System.IO hiding (hPutStr, hPutStrLn, hGetLine, hGetContents) import System.IO.UTF8 connectserver :: HostName -- ^ Remote hostname, or localhost -> String -- ^ Port number or name -> IO Handle connectserver hostname port = withSocketsDo $ do -- withSocketsDo is required on Windows -- Look up the hostname and port. Either raises an exception -- or returns a nonempty list. First element in that list -- is supposed to be the best option. addrinfos <- getAddrInfo Nothing (Just hostname) (Just port) let serveraddr = head addrinfos -- Establish a socket for communication sock <- socket (addrFamily serveraddr) Stream defaultProtocol -- Mark the socket for keep-alive handling since it may be idle -- for long periods of time setSocketOption sock KeepAlive 1 -- Connect to server connect sock (addrAddress serveraddr) -- Make a Handle out of it for convenience h <- socketToHandle sock ReadWriteMode -- Were going to set buffering to LineBuffering and then -- explicitly call hFlush after each message, below, so that -- messages get logged immediately hSetBuffering h LineBuffering return h sendid :: Handle -> String -> IO String sendid h id = do hPutStr h id -- Make sure that we send data immediately hFlush h -- Retrieve results hGetLine h The code portions in connectserver are from this chapter of Real World Haskell book where they say: When dealing with TCP data, it's often convenient to convert a socket into a Haskell Handle. We do so here, and explicitly set the buffering – an important point for TCP communication. Next, we set up lazy reading from the socket's Handle. For each incoming line, we pass it to handle. After there is no more data – because the remote end has closed the socket – we output a message about that. Since hGetContents blocks until the server closes the socket on the other side, I used hGetLine instead. It satisfied me before I decided to implement multiline output to client. I wouldn't like the server to close a socket every time it finishes sending multiline text. The only simple idea I have at the moment is to count the number of linefeeds and stop reading lines after two subsequent linefeeds. Do you have any better suggestions? Thanks.

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• sending and receiving with sockets in java?

  - by Darksole

  I am working on sending and receiving from clients and servers in java, and am stumped at the moment. the client socket is to contact a server at “localhost” port 4321. The client will receive a string from the server and alternate spelling the contents of this string with the server. For example, given the string “Bye Bye”, the client (which always begins sending the first letter) sends “B”, receives “y”, sends “e”, receives “ ”, sends “B”, receives “y”, sends “e”, and receives “done!”, which is the string that either client or server will send after the last letter from the original string is received. After “done!” is transmitted, both client and server close their communications. How would i go about getting the first string and then going back and forth sending and reciving letters that make the string, and when finished either send or get done!? import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.io.PrintWriter; import java.net.Socket; import java.net.UnknownHostException; import java.util.Scanner; public class Program2 { public static void goClient() throws UnknownHostException, IOException{ String server = "localhost"; int port = 4321; Socket socket = new Socket(server, port); InputStream inStream = socket.getInputStream(); OutputStream outStream = socket.getOutputStream(); Scanner in = new Scanner(inStream); PrintWriter out = new PrintWriter(outStream, true); String rec = ""; if(in.hasNext()){ rec = in.nextLine(); } char[] array = new char[rec.length()]; for(int i = 0; i < rec.length(); i++){ array[i] = rec.charAt(i); } while(in.hasNext()){ for(int x = 0; x < array.length + 1; x+=2){ String str = in.nextLine(); str = Character.toString(array[x]); out.println(str); } in.close(); socket.close(); } } }

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• What about buffering FileInputStream?

  - by Pregzt

  I have a piece of code that reads hell of a lot (hundreds of thousand) of relatively small files (couple of KB) from the local file system in a loop. For each file there is a java.io.FileInputStream created to read the content. The process its very slow and take ages. Do you think that wrapping the FIS into java.io.BufferedInputStream would make a significant difference?

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• Page not redirecting properly(php)

  - by user225269

  I want to do the login page this way so that I won't be having trouble posting the username in the userpage. But everytime I try to access login.php. I get an error in firefox, that the page is not redirecting properly. What do I do? This works when I separate them into two. Into something like, login.php and verifylogin.php as the form action. But if I do it like this, I get redirection errors: <?php $host="localhost"; $username="root"; $password="nitoryolai123$%^"; $db_name="school"; $tbl_name="users"; mysql_connect("$host", "$username", "$password")or die("cannot connect"); mysql_select_db("$db_name")or die("cannot select DB"); $uname = mysql_real_escape_string($_POST['username']); $pword = mysql_real_escape_string($_POST['password']); $SQL = "SELECT * FROM users WHERE username = '$uname' AND password = '$pword'"; $result = mysql_query($SQL); $num_rows = mysql_num_rows($result); if ($result) { if ($num_rows > 0) { session_start(); $_SESSION['login'] = "1"; header ("Location: userpage.php"); } else { session_start(); $_SESSION['login'] = ""; header ("Location: login.php"); } } else { $errorMessage = "Error logging on"; } ?> <tr> <form name="form1" method="post" action="login.php"> <td> <table> <tr> <td><strong><font size="2">Login User</strong></td> </tr> <tr> <td width="30" height="35"><font size="2">Username:</td> <td width="30"><input name="username" type="text" id="username" maxlength="17"></td> </tr> <tr> <td width="30" height="35" ><font size="2">Password:</td> <td width="30"><input name="password" type="password" id="password" maxlength="17"></td> </tr> <td><td align="right" width="30"><input type="submit" name="Submit" value="Submit" /></td> <td><input type="reset" name="Reset" value="Reset"></td></td> </tr> </form> please help, thanks.

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• LibPNG + Boost::GIL: png_infopp_NULL not found

  - by Viet

  Hi, I always get this error when trying to compile my file with Boost::GIL PNG IO support: (I'm running Mac OS X Leopard and Boost 1.42, LibPNG 1.4) /usr/local/include/boost/gil/extension/io/png_io_private.hpp: In member function 'void boost::gil::detail::png_reader::init()': /usr/local/include/boost/gil/extension/io/png_io_private.hpp:155: error: 'png_infopp_NULL' was not declared in this scope /usr/local/include/boost/gil/extension/io/png_io_private.hpp:160: error: 'png_infopp_NULL' was not declared in this scope /usr/local/include/boost/gil/extension/io/png_io_private.hpp: In destructor 'boost::gil::detail::png_reader::~png_reader()': /usr/local/include/boost/gil/extension/io/png_io_private.hpp:174: error: 'png_infopp_NULL' was not declared in this scope /usr/local/include/boost/gil/extension/io/png_io_private.hpp: In member function 'void boost::gil::detail::png_reader::apply(const View&)': /usr/local/include/boost/gil/extension/io/png_io_private.hpp:186: error: 'int_p_NULL' was not declared in this scope /usr/local/include/boost/gil/extension/io/png_io_private.hpp: In member function 'void boost::gil::detail::png_reader_color_convert<CC>::apply(const View&)': /usr/local/include/boost/gil/extension/io/png_io_private.hpp:228: error: 'int_p_NULL' was not declared in this scope /usr/local/include/boost/gil/extension/io/png_io_private.hpp: In member function 'void boost::gil::detail::png_writer::init()': /usr/local/include/boost/gil/extension/io/png_io_private.hpp:317: error: 'png_infopp_NULL' was not declared in this scope

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• How to properly close a UDT server in Netty 4

  - by Steffen

  I'm trying to close my UDT server (Netty 4.0.5.Final) with shutDownGracefully() and reopen it on the same port. Unfortunately, I always get the socket exception below although it waits until the future has completed. I also added the socket option SO_REUSEADDR. What is the proper way to do this? Exception in thread "main" com.barchart.udt.ExceptionUDT: UDT Error : 5011 : another socket is already listening on the same UDP port : listen0:listen [id: 0x323d3939] at com.barchart.udt.SocketUDT.listen0(Native Method) at com.barchart.udt.SocketUDT.listen(SocketUDT.java:1136) at com.barchart.udt.net.NetServerSocketUDT.bind(NetServerSocketUDT.java:66) at io.netty.channel.udt.nio.NioUdtAcceptorChannel.doBind(NioUdtAcceptorChannel.java:71) at io.netty.channel.AbstractChannel$AbstractUnsafe.bind(AbstractChannel.java:471) at io.netty.channel.DefaultChannelPipeline$HeadHandler.bind(DefaultChannelPipeline.java:1006) at io.netty.channel.DefaultChannelHandlerContext.invokeBind(DefaultChannelHandlerContext.java:504) at io.netty.channel.DefaultChannelHandlerContext.bind(DefaultChannelHandlerContext.java:487) at io.netty.channel.ChannelDuplexHandler.bind(ChannelDuplexHandler.java:38) at io.netty.handler.logging.LoggingHandler.bind(LoggingHandler.java:254) at io.netty.channel.DefaultChannelHandlerContext.invokeBind(DefaultChannelHandlerContext.java:504) at io.netty.channel.DefaultChannelHandlerContext.bind(DefaultChannelHandlerContext.java:487) at io.netty.channel.DefaultChannelPipeline.bind(DefaultChannelPipeline.java:848) at io.netty.channel.AbstractChannel.bind(AbstractChannel.java:193) at io.netty.bootstrap.AbstractBootstrap$2.run(AbstractBootstrap.java:321) at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:354) at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:366) at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:101) at java.lang.Thread.run(Thread.java:724) A small test program demonstration the problem: public class MsgEchoServer { public static class MsgEchoServerHandler extends ChannelInboundHandlerAdapter { } public void run() throws Exception { final ThreadFactory acceptFactory = new UtilThreadFactory("accept"); final ThreadFactory connectFactory = new UtilThreadFactory("connect"); final NioEventLoopGroup acceptGroup = new NioEventLoopGroup(1, acceptFactory, NioUdtProvider.MESSAGE_PROVIDER); final NioEventLoopGroup connectGroup = new NioEventLoopGroup(1, connectFactory, NioUdtProvider.MESSAGE_PROVIDER); try { final ServerBootstrap boot = new ServerBootstrap(); boot.group(acceptGroup, connectGroup) .channelFactory(NioUdtProvider.MESSAGE_ACCEPTOR) .option(ChannelOption.SO_BACKLOG, 10) .option(ChannelOption.SO_REUSEADDR, true) .handler(new LoggingHandler(LogLevel.INFO)) .childHandler(new ChannelInitializer<UdtChannel>() { @Override public void initChannel(final UdtChannel ch) throws Exception { ch.pipeline().addLast(new MsgEchoServerHandler()); } }); final ChannelFuture future = boot.bind(1234).sync(); } finally { acceptGroup.shutdownGracefully().syncUninterruptibly(); connectGroup.shutdownGracefully().syncUninterruptibly(); } new MsgEchoServer().run(); } public static void main(final String[] args) throws Exception { new MsgEchoServer().run(); } }

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• Reduce the I/O priority of Windows Backup (Windows Server 2008 R2)

  - by HelloSam

  I have a PostgreSQL running on Windows Server 2008 R2 x64 box. And I have scheduled a backup everyday from the RAID 1 DB disk to a dedicated standalone disk. They are SAS 15k on Dell PERC 6i. I am using the built-in Windows Server Backup for purpose. The problem is, whenever the backup process is kicked in, the database performance is hogged. I would say almost a 10x of performance reduction. From the resource monitor, the disk queue is in the double digit range when backing up, and less than 1 during the day. The disk activity is like ~30-50MB/s during backup, so I guess the hardware is acting normally, though wbengine.exe takes up most of the portions. I think reduce the IO priority of the backup process would be an answer, but I couldn't find a way to. Tuning process CPU priority does not seems to help.

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• Large file copy from NFS to local disk performance drop

  - by Bernhard

  I'm trying to copy a 200GB file from an NFS mount to a local disk. The local disk is an XFS filesystem on a LVM on top of a RAID 5 system (hardware RAID controler). I'm using rsync to monitor the transfer speed. At the beginning the IO speed is about 200MB/s, stable for the first 18GB. But then the performance drops by a factor of 10-20 and never recovers to the initial rate. Sometimes it reaches about 50-100MB/s but just for a few seconds and then the process seems to hang for a bit. At the same time all file-stat operations on the target filesystem are blocking for a long time (minutes). Also interrupting the copy process blocks for several minutes, a sub-sequent delete of the partly copied file takes also several minutes. Any ideas what could be causing this?

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• How to arrange 2 SSD with 2 SATA?

  - by alfish

  I like to have best io performance as well as good capaciyy and reliability out of a server that hosts a busy forum, which involves loads of static files download. I am wondering what is the best plan to format and use the disks given that the server has only 4 disk bays and I have 2 SSD and 2 SATA disks at hand. I am currently thinking about putting the disks in RAID 10 so that SSD contains /var/lib/mysql as well as most of the OS (Likely to be Debian) and SATA disk to contain /path/to/static/files. However I'd like to hear your expert opinion on this. Thanks

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• Should I store my code/projects on my SSD or my secondary drive?

  - by user37467

  I just got a new box. It has an SSD for the primary drive, and a 1TB SATA for the secondary drive. I'm going to run windows and my binaries on the SSD and keep all my downloads/documents/music/etc on the secondary drive. My question is should I also keep my Visual Studio Projects and code on the SSD or keep them on the secondary drive? The faster SSD would presumably be better for compiling and indexed searches, but would it be better to keep it on the 2nd drive for a more parallel disk IO situation?

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• How do I set up DNS with nic.io to point to an AWS EC2 server?

  - by Chad Johnson

  I purchased a domain one week ago via nic.io. I have elected to provide my own DNS [because they provided no other option]. I'm trying to point my .io domain at my EC2 server instance. I've allocated an elastic IP and associated it with the instance. I can SSH into the instance and access point 80 via the IP address just fine. The IP is 54.235.201.241. nic.io support said the following: "You have selected to provide your own DNS and therefore if there is an issue with the set-up of the name servers you will need to contact your DNS provider." So, I created a Hosted Zone via Route 53 in AWS. This created NS and SOA records. I then set the Primary and Secondary servers at nic.io's domain admin page to the SOA record domains. Additionally, I set the optional servers to the NS domains. I did this two days ago, and I can't access the server via the domain. I ran a DNS check here...still not sure what I need to do: http://mydnscheck.com/?domain=chadjohnson.io&ns1=&ns2=&ns3=&ns4=&ns5=&ns6=. I have no idea what I'm supposed to do. Does anyone have any ideas?

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• How to keep subtree removal (`rm -rf`) from starving other processes for Disk I/O?

  - by David Eyk

  We have a very large (multi-GB) Nginx cache directory for a busy site, which we occasionally need to clear all at once. I've solved this in the past by moving the cache folder to a new path, making a new cache folder at the old path, and then rm -rfing the old cache folder. Lately, however, when I need to clear the cache on a busy morning, the I/O from rm -rf is starving my server processes of disk access, as both Nginx and the server it fronts for are read-intensive. I can watch the load average climb while the CPUs sit idle and rm -rf takes 98-99% of Disk IO in iotop. I've tried ionice -c 3 when invoking rm, but it seems to have no appreciable effect on the observed behavior. Is there any way to tame rm -rf to share the disk more? Do I need to use a different technique that will take its cues from ionice? Update: The filesystem in question is an AWS EC2 instance store (the primary disk is EBS). The /etc/fstab entry looks like this: /dev/xvdb /mnt auto defaults,nobootwait,comment=cloudconfig 0 2

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• one 16K random read I/O issues 2 scsi I/O (16K and 4K) requests in linux

  - by hiroyuki

  I noticed weird issue when benchmarking random read I/O for files in linux (2.6.18). The Benchmarking program is my own program and it simply keeps reading 16KB of a file from a random offset. I traced I/O behavior at system call level and scsi level by systemtap and I noticed that one 16KB sysread issues 2 scsi I/Os as following. SYSPREAD random(8472) 3, 0x16fc5200, 16384, 128137183232 SCSI random(8472) 0 1 0 0 start-sector: 226321183 size: 4096 bufflen 4096 FROM_DEVICE 1354354008068009 SCSI random(8472) 0 1 0 0 start-sector: 226323431 size: 16384 bufflen 16384 FROM_DEVICE 1354354008075927 SYSPREAD random(8472) 3, 0x16fc5200, 16384, 21807710208 SCSI random(8472) 0 1 0 0 start-sector: 1889888935 size: 4096 bufflen 4096 FROM_DEVICE 1354354008085128 SCSI random(8472) 0 1 0 0 start-sector: 1889891823 size: 16384 bufflen 16384 FROM_DEVICE 1354354008097161 SYSPREAD random(8472) 3, 0x16fc5200, 16384, 139365318656 SCSI random(8472) 0 1 0 0 start-sector: 254092663 size: 4096 bufflen 4096 FROM_DEVICE 1354354008100633 SCSI random(8472) 0 1 0 0 start-sector: 254094879 size: 16384 bufflen 16384 FROM_DEVICE 1354354008111723 SYSPREAD random(8472) 3, 0x16fc5200, 16384, 60304424960 SCSI random(8472) 0 1 0 0 start-sector: 58119807 size: 4096 bufflen 4096 FROM_DEVICE 1354354008120469 SCSI random(8472) 0 1 0 0 start-sector: 58125415 size: 16384 bufflen 16384 FROM_DEVICE 1354354008126343 As shown above, one 16KB pread issues 2 scsi I/Os. (I traced scsi io dispatching with probe scsi.iodispatching. Please ignore values except for start-sector and size.) One scsi I/O is 16KB I/O as requested from the application and it's OK. The thing is the other 4KB I/O which I don't know why linux issues that I/O. of course, I/O performance is degraded by the weired 4KB I/O and I am having trouble. I also use fio (famous I/O benchmark tool) and noticed the same issue, so it's not from the application. Does anybody know what is going on ? Any comments or advices are appreciated. Thanks

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• High disk I/O activity in CentOS server

  - by triiim

  I have about 16 websites in a CentOS dedicated, and I am having some problems on high traffic hours, it seems to be a high disk I/O activity causing a general slowdown. I've installed atop and this is what I see on the bottom (the server has been restarted thats why the values are so low): *** system and process activity since boot *** PID RDDSK WRDSK WCANCL DSK CMD 1/18 2176 1.7G 7.3G 854.4M 39 mysqld 671 1248K 3.0G 0K 13 flush-8:0 566 0K 1.1G 0K 5 jbd2/sda2-8 2401 124.2M 529.1M 22408K 3 crond 2032 2.2G 502.0M 0K 12 nginx 2360 425.8M 115.3M 4188K 2 httpd flush-8:0 and jbd2/sda2-8 are the processes I see with iotop using 99% on the IO column, and they are the processes that write the most on the hdd (after mysql). From what I saw in google this could be caused by some ext4 related bug, the current kernel is: Linux srvr.com 2.6.32-71.29.1.el6.x86_64 #1 SMP Mon Jun 27 19:49:27 BST 2011 x86_64 x86_64 x86_64 GNU/Linux I asked the hosting support to update the kernel and they tried but they now say that the server wont boot with the new installed kernel and they had to go back to the previous, they are not helping very much. Does someone has any idea how could I solve the high disk usage caused by flush-8:0 and jbd2/sda2-8 processes?

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• Input/output error reading USB backup drive on CentOS 6.4

  - by Kev

  I'm suddenly seeing some strange behaviour on our USB backup drive that doesn't make sense to me: (2013-10-21 14:58:23 [root@newdc /]$ cd /mnt/backup/ (2013-10-21 14:59:03 [root@newdc backup]$ ls -la ls: reading directory .: Input/output error total 0 (2013-10-21 14:59:05 [root@newdc backup]$ df -h /mnt/backup Filesystem Size Used Avail Use% Mounted on /dev/sda1 917G 843G 28G 97% /mnt/backup How is it possible for the OS to know how much is in use, but I can't ls any of it as root? Or more to the point, what problem does this indicate? /var/log/messages said this: Oct 21 14:57:54 g5 kernel: EXT4-fs error (device sda1): ext4_journal_start_sb: Detected aborted journal Oct 21 14:57:54 g5 kernel: EXT4-fs (sda1): Remounting filesystem read-only But...read-only is something different than 'throw an io error'... After unmounting to try fsck on it, I had someone on-site look at it, and the drive was not spun up, and had a slow-flashing light, which I believe means it was in a power-suspend mode. So I had them unplug and replug the USB cable, and now (before remounting) it says: fsck from util-linux-ng 2.17.2 e2fsck 1.41.12 (17-May-2010) /dev/sda1: clean, 2805106/61046784 files, 181934167/244182016 blocks I then mount it and now ls works and df reports: Filesystem Size Used Avail Use% Mounted on /dev/sda1 917G 680G 191G 79% /mnt/backup What would cause it to go into such a state without being asked to? Why all the weird behaviour, and now it appears to not be corrupt?

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