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• Clustered index on frequently changing reference table of one or more foreign keys

  - by Ian

  My specific concern is related to the performance of a clustered index on a reference table that has many rapid inserts and deletes. Table 1 "Collection" collection_pk int (among other fields) Table 2 "Item" item_pk int (among other fields) Reference Table "Collection_Items" collection_pk int, item_pk int (combined primary key) Because the primary key is composed of both pks, a clustered index is created and the data physically ordered in the table according to the combined keys. I have many users creating and deleting collections and adding and removing items to those collections very frequently affecting the "Collection_Items" table, and its clustered index. QUESTION PART: Since the "Collection_Items" table is so dynamic, wouldn't there be a big performance hit on constantly resorting the table rows because of the clustered index ? If yes, what should I do to minimize this ?

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• Benchmark of Java Try/Catch Block

  - by hectorg87

  I know that going into a catch block has some significance cost when executing a program, however, I was wondering if entering a try{} block also had any impact so I started looking for an answer in google with many opinions, but no benchmarking at all. Some answers I found were: Java try/catch performance, is it recommended to keep what is inside the try clause to a minimum? Try Catch Performance Java Java try catch blocks However they didn't answer my question with facts, so I decided to try it for myself. Here's what I did. I have a csv file with this format: host;ip;number;date;status;email;uid;name;lastname;promo_code; where everything after status is optional and will not even have the corresponding ; , so when parsing a validation has to be done to see if the value is there, here's where the try/catch issue came to my mind. The current code that in inherited in my company does this: StringTokenizer st=new StringTokenizer(line,";"); String host = st.nextToken(); String ip = st.nextToken(); String number = st.nextToken(); String date = st.nextToken(); String status = st.nextToken(); String email = ""; try{ email = st.nextToken(); }catch(NoSuchElementException e){ email = ""; } and it repeats what it's done for email with uid, name, lastname and promo_code. and I changed everything to: if(st.hasMoreTokens()){ email = st.nextToken(); } and in fact it performs faster. When parsing a file that doesn't have the optional columns. Here are the average times: --- Trying:122 milliseconds --- Checking:33 milliseconds however, here's what confused me and the reason I'm asking: When running the example with values for the optional columns in all 8000 lines of the CSV, the if() version still performs better than the try/catch version, so my question is Does really the try block does not have any performance impact on my code? The average times for this example are: --- Trying:105 milliseconds --- Checking:43 milliseconds Can somebody explain what's going on here? Thanks a lot

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• Which low level tasks can be accomplished on the JVM, but not expressed in java?

  - by mike g

  Which useful (for performance or otherwise) constructions are valid bytecode, but not expressable in Java?

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• Video chat application : Which technology to choose ?

  - by WarDoGG

  I have to undertake a project which is to make a video chat application. The video has to be streamed from one location and can be viewed by multiple people spread out over the globe. Performance is really an issue and a delay of more than 2-3 seconds is unacceptable. From what i gather, this can be done in Flex and also in JAVA. Any performance issues and caveats with a particular approach ? I would really like the pros to comment on this and guide me through. Will be very very helpful. Are there any open source libraries available for video recording in flash / JAVA which i can integrate into my app and customize according to my needs ?

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• What is the best solution to replace a new memory allocator in an existing code?

  - by O. Askari

  During the last few days I've gained some information about memory allocators other than the standard malloc(). There are some implementations that seem to be much better than malloc() for applications with many threads. For example it seems that tcmalloc and ptmalloc have better performance. I have a C++ application that uses both malloc and new operators in many places. I thought replacing them with something like ptmalloc may improve its performance. But I wonder how does the new operator act when used in C++ application that runs on Linux? Does it use the standard behavior of malloc or something else? What is the best way to replace the new memory allocator with the old one in the code? Is there any way to override the behavior or new and malloc or do I need to replace all the calls to them one by one?

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• Is there any harm in running session_start() multiple times as the page request is being built (in p

  - by sprugman

  Presumably there's some tiny performance hit, but beyond that?

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• which is better, creating a view or a new table?

  - by Carson

  I have some demanding mysql queries that are needed to grap same datasets from several mysql tables. I am thinking of creating a table or view to gather all demanding columns from other tables, so as to increase performance. If I create that table, I may need to do extra insert / update / delete operation each time other tables updated. if I create view, I am worrying if the performance can be greatly improved. Because data from other tables are changing very frequently. Most likely, the view may need to be created first everytime before selecting it. Any ideas? e.g. how to cache? other extra measures I can do?

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• Checking exception before using GETITEMBYID()

  - by ps123

  Hello, I am getting item by getiembyid...but I want to check before using it that whether item exist or not...I don't want to use query as main purpose of using Getitembyid is performance.....any idea how to achieve this... itemid = Response.QueryString["loc"]; SPList mylist = myweb.GetList(SPUrlUtility.CombineUrl(myweb.ServerRelativeUrl, "/Lists/Location")); //now id itemid does not exist it throws exception...so i want to check before using following statement that itemid exist...I know i can check throw SPQuery but as i said above because of performance issue only i m using itemid.... SPListItem myitem = mylist.GetItemById(Convert.ToInt32(itemid)); Any idea how to achieve this?

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• Marvell C++ compiler (for Windows CE) for building Qt

  - by vnm

  Hello, I was able to build Qt 4.5 for Windows CE (ARM4VI) using MS VisualC++ compiler. Now, I am trying to compile Qt 4.5 for Windows CE 5.0 using Marvel C++ compiler v 2.2 (former Intel C++ compiler for XScale architecture) for achieving some performance benefit. It seems, that this compiler not officially supported for building Qt by trolltech (no appropriate mkspec in mkspec's folder of Qt folder). So, my questions: Is it worth to trying build Qt by this compiler for achieving performance enhancement ? Is there any way for building Qt using Marvell C++ compiler (by creating my own mkspec or something like that)?

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• List filtering: list comprehension vs. lambda + filter

  - by Agos

  I happened to find myself having a basic filtering need: I have a list and I have to filter it by an attribute of the items. My code looked like this: list = [i for i in list if i.attribute == value] But then i thought, wouldn't it be better to write it like this? filter(lambda x: x.attribute == value, list) It's more readable, and if needed for performance the lambda could be taken out to gain something. Question is: are there any caveats in using the second way? Any performance difference? Am I missing the Pythonic Way™ entirely and should do it in yet another way (such as using itemgetter instead of the lambda)? Thanks in advance

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• mysql twitter/facebook like status feed

  - by barjonah

  Hi, I have two tables. One named status like this... user_id | status --------+----------- 1 | random status from user 1 2 | random status from user 2 3 | random message from user 3 4 | staus from user 4 1 | second status for user1 etc... and another named users_following like this... user_id | is_following --------+----------- 1 | 2 1 | 3 2 | 1 3 | 2 meaning that user 1 is following both users 2 and 3 etc... So, let's say I chose user 1. What is the best query (performance wise) to show the status updates of users that user 1 is following, in this case users 2 and 3 currently I have something like SELECT * from status WHERE user_id IN(SELECT is_following FROM users_following WHERE user_id='1') LIMIT 0,5 but I don't think this is good for performance if a user was following thousands+ of users

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• How do you visualize difference between O(log n) and O(n log n)?

  - by Passionate programmer

  Binary search has a average case performance as O(log n) and Quick Sort with O(n log n) is O(n log n) is same as O(n) + O(log n)

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• Sql Server as logging, best connection practise

  - by ozz

  I'm using SqlServer as logging. Yes this is wrong decision, there are better dbs for this requirement. But I have no other option for now. Logging interval is 3 logs per second. So I've static Logger class and it has static Log method. Using "Open Connection" as static member is better for performance. But what is the best implemantation of it? This is not that I know. public static class OzzLogger { static SqlConnection Con; static OzzLogger() { Con=ne SqlConnection(....); Con.Open(); } public static void Log(....) { Con.ExecuteSql(......); } } UPDATE I asked because of my old information. People say "connection pooling performance is enough". If there is no objection I'm closing the issue :)

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• How would I benchmark an Android Application?

  - by davs

  How would I benchmark or profile the performance of an Android application?

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• How expensive are method calls in .net

  - by Andrew

  What is the relative performance cost of calling a method over in-line code?

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• Why is numpy c extension slow?

  - by Bitwise

  I am working on large numpy arrays, and some native numpy operations are too slow for my needs (for example simple operations such as "bitwise" A&B). I started looking into writing C extensions to try and improve performance. As a test case, I tried the example given here, implementing a simple trace calculation. I was able to get it to work, but was surprised by the performance: for a (1000,1000) numpy array, numpy.trace() was about 1000 times faster than the C extension! This happens whether I run it once or many times. Is this expected? Is the C extension overhead that bad? Any ideas how to speed things up?

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• C and C++: Array element access pointer vs int

  - by begun

  Is there a performance difference if you either do myarray[ i ] or store the adress of myarray[ i ] in a pointer?

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• Javascript === vs == : Does it matter which "equal" operator I use?

  - by bcasp

  I'm using JSLint to go through some horrific JavaScript at work and it's returning a huge number of suggestions to replace == with === when doing things like comparing 'idSele_UNVEHtype.value.length == 0' inside of an if statement. I'm basically wondering if there is a performance benefit to replacing == with ===. Any performance improvement would probably be welcomed as there are hundreds (if not thousands) of these comparison operators being used throughout the file. I tried searching for relevant information to this question, but trying to search for something like '=== vs ==' doesn't seem to work so well with search engines...

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• Does the order of the columns in a SELECT statement make a difference?

  - by Frank Computer

  This question was inspired by a previous question posted on SO, "Does the order of the WHERE clause make a differnece?". Would it improve a SELECT statement's performance if the the columns used in the WHERE section are placed at the begining of the SELECT statement? example: SELECT customer.id, transaction.id, transaction.efective_date, transaction.a, [...] FROM customer, transaction WHERE customer.id = transaction.id; I do know that limiting the list of columns to only the needed ones in a SELECT statement improves performance as opposed to using SELECT * because the current list is smaller.

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• What is the best way to partition large tables in SQL Server?

  - by RyanFetz

  In a recent project the "lead" developer designed a database schema where "larger" tables would be split across two seperate databases with a view on the main database which unioned the two seperate database-tables together. The main database is what the application was driven off of so these tables looked and felt like ordinary tables (except some quirkly things around updating). This seemed like a HUGE performance problem. We do see problems with performance around these tables but nothing to make him change his mind about his design. Just wondering what is the best way to do this, or if it is even worth doing?

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• Any reason NOT to slap the 'synchronized' keyword everywhere?

  - by unknown

  In my java project, almost every non-static method I've written is synchronized. I've decided to fix up some code today, by removing most of the synchronized keywords. Right there I created several threading issues that took quite a while to fix, with no increase in performance. In the end I reverted everything. I don't see anyone else writing code with "synchronized" everywhere. So is there any reason I shouldn't have "synchronized" everywhere? What if I don't care too much about performance (ie. the method isn't called more than once every few seconds)?

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• enableviewstatemac=true

  - by domineer

  Does setting enableviewstatemac to "true" affects the site's performance? Could you give me some explanation?

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• Enable Php Fastcgi and Get 500 Internal Server Error (Lighttpd)

  - by skycrew

  anyone can help me? I just got this problem today. Before this my site running smooth with Fastcgi enable but now its show 500 internal server error with below logs. I need to disable php fastcgi in LxAdmin so that my visitor can access my site but when I disable php fastgi, my web performance is very slow with high load to server. I also include the performance screenshot. What should I do? This are the error log I got: 2010-06-16 21:59:52: (mod_cgi.c.584) cgi died, pid: 24055 2010-06-16 21:59:52: (mod_cgi.c.584) cgi died, pid: 21622 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 3342 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3207) child exited, pid: 3342 status: 0 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 836 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24447 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 860 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24447 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 836 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24447 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 878 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24447 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 878 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24447 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 878 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_cgi.c.584) cgi died, pid: 22325 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24447 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 852 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_cgi.c.584) cgi died, pid: 24032 2010-06-16 21:59:52: (mod_cgi.c.584) cgi died, pid: 20402 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 3336 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 2010-06-16 21:59:52: (mod_fastcgi.c.3207) child exited, pid: 3336 status: 0 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 855 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 for /index.php , closing connection 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24448 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 860 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 for /index.php , closing connection 2010-06-16 21:59:52: (mod_cgi.c.1231) cgi died ? 2010-06-16 21:59:53: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24448 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 2010-06-16 21:59:53: (mod_fastcgi.c.3254) response not received, request sent: 860 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 for /index.php , closing connection 2010-06-16 21:59:53: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24448 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 2010-06-16 21:59:53: (mod_fastcgi.c.3254) response not received, request sent: 878 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 for /index.php , closing connection 2010-06-16 21:59:53: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24448 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 2010-06-16 21:59:53: (mod_fastcgi.c.3254) response not received, request sent: 860 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 for /index.php , closing connection 2010-06-16 21:59:53: (mod_fastcgi.c.1731) connect failed: Connection refused on unix:/var/tmp/lighttpd/php.socket.lyrics-hub.com.3333-1 2010-06-16 21:59:53: (mod_fastcgi.c.2885) backend died; we'll disable it for 5 seconds and send the request to another backend instead: reconnects: 0 load: 1 2010-06-16 21:59:56: (server.c.1470) server stopped by UID = 0 PID = 24439 2010-06-16 22:00:23: (log.c.75) server started Performance Graph as below:- http://img404.imageshack.us/img404/3498/memorylxadmin.jpg

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• Enable Php Fastcgi and Get 500 Internal Server Error (Lighttpd)

  - by skycrew

  Hello everyone, anyone can help me? I just got this problem today. Before this my site running smooth with Fastcgi enable but now its show 500 internal server error with below logs. I need to disable php fastcgi in LxAdmin so that my visitor can access my site but when I disable php fastgi, my web performance is very slow with high load to server. I also include the performance screenshot. What should I do? This are the error log I got: 2010-06-16 21:59:52: (mod_cgi.c.584) cgi died, pid: 24055 2010-06-16 21:59:52: (mod_cgi.c.584) cgi died, pid: 21622 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 3342 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3207) child exited, pid: 3342 status: 0 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 836 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24447 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 860 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24447 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 836 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24447 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 878 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24447 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 878 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24447 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 878 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_cgi.c.584) cgi died, pid: 22325 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24447 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 852 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-1 for /index.php , closing connection 2010-06-16 21:59:52: (mod_cgi.c.584) cgi died, pid: 24032 2010-06-16 21:59:52: (mod_cgi.c.584) cgi died, pid: 20402 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 3336 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 2010-06-16 21:59:52: (mod_fastcgi.c.3207) child exited, pid: 3336 status: 0 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 855 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 for /index.php , closing connection 2010-06-16 21:59:52: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24448 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 2010-06-16 21:59:52: (mod_fastcgi.c.3254) response not received, request sent: 860 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 for /index.php , closing connection 2010-06-16 21:59:52: (mod_cgi.c.1231) cgi died ? 2010-06-16 21:59:53: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24448 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 2010-06-16 21:59:53: (mod_fastcgi.c.3254) response not received, request sent: 860 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 for /index.php , closing connection 2010-06-16 21:59:53: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24448 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 2010-06-16 21:59:53: (mod_fastcgi.c.3254) response not received, request sent: 878 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 for /index.php , closing connection 2010-06-16 21:59:53: (mod_fastcgi.c.2462) unexpected end-of-file (perhaps the fastcgi process died): pid: 24448 socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 2010-06-16 21:59:53: (mod_fastcgi.c.3254) response not received, request sent: 860 on socket: unix:/var/tmp/lighttpd/php.socket.lyrics.skycrewz.net.3333-0 for /index.php , closing connection 2010-06-16 21:59:53: (mod_fastcgi.c.1731) connect failed: Connection refused on unix:/var/tmp/lighttpd/php.socket.lyrics-hub.com.3333-1 2010-06-16 21:59:53: (mod_fastcgi.c.2885) backend died; we'll disable it for 5 seconds and send the request to another backend instead: reconnects: 0 load: 1 2010-06-16 21:59:56: (server.c.1470) server stopped by UID = 0 PID = 24439 2010-06-16 22:00:23: (log.c.75) server started Performance Graph as below:- http://img404.imageshack.us/img404/3498/memorylxadmin.jpg

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• KVM guest io is much slower than host io: is that normal?

  - by Evolver

  I have a Qemu-KVM host system setup on CentOS 6.3. Four 1TB SATA HDDs working in Software RAID10. Guest CentOS 6.3 is installed on separate LVM. People say that they see guest performance almost equal to host performance, but I don't see that. My i/o tests are showing 30-70% slower performance on guest than on host system. I tried to change scheduler (set elevator=deadline on host and elevator=noop on guest), set blkio.weight to 1000 in cgroup, change io to virtio... But none of these changes gave me any significant results. This is a guest .xml config part: <disk type='file' device='disk'> <driver name='qemu' type='raw'/> <source file='/dev/vgkvmnode/lv2'/> <target dev='vda' bus='virtio'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/> </disk> There are my tests: Host system: iozone test # iozone -a -i0 -i1 -i2 -s8G -r64k random random KB reclen write rewrite read reread read write 8388608 64 189930 197436 266786 267254 28644 66642 dd read test: one process and then four simultaneous processes # dd if=/dev/vgkvmnode/lv2 of=/dev/null bs=1M count=1024 iflag=direct 1073741824 bytes (1.1 GB) copied, 4.23044 s, 254 MB/s # dd if=/dev/vgkvmnode/lv2 of=/dev/null bs=1M count=1024 iflag=direct skip=1024 & dd if=/dev/vgkvmnode/lv2 of=/dev/null bs=1M count=1024 iflag=direct skip=2048 & dd if=/dev/vgkvmnode/lv2 of=/dev/null bs=1M count=1024 iflag=direct skip=3072 & dd if=/dev/vgkvmnode/lv2 of=/dev/null bs=1M count=1024 iflag=direct skip=4096 1073741824 bytes (1.1 GB) copied, 14.4528 s, 74.3 MB/s 1073741824 bytes (1.1 GB) copied, 14.562 s, 73.7 MB/s 1073741824 bytes (1.1 GB) copied, 14.6341 s, 73.4 MB/s 1073741824 bytes (1.1 GB) copied, 14.7006 s, 73.0 MB/s dd write test: one process and then four simultaneous processes # dd if=/dev/zero of=test bs=1M count=1024 oflag=direct 1073741824 bytes (1.1 GB) copied, 6.2039 s, 173 MB/s # dd if=/dev/zero of=test bs=1M count=1024 oflag=direct & dd if=/dev/zero of=test2 bs=1M count=1024 oflag=direct & dd if=/dev/zero of=test3 bs=1M count=1024 oflag=direct & dd if=/dev/zero of=test4 bs=1M count=1024 oflag=direct 1073741824 bytes (1.1 GB) copied, 32.7173 s, 32.8 MB/s 1073741824 bytes (1.1 GB) copied, 32.8868 s, 32.6 MB/s 1073741824 bytes (1.1 GB) copied, 32.9097 s, 32.6 MB/s 1073741824 bytes (1.1 GB) copied, 32.9688 s, 32.6 MB/s Guest system: iozone test # iozone -a -i0 -i1 -i2 -s512M -r64k random random KB reclen write rewrite read reread read write 524288 64 93374 154596 141193 149865 21394 46264 dd read test: one process and then four simultaneous processes # dd if=/dev/mapper/VolGroup-lv_home of=/dev/null bs=1M count=1024 iflag=direct skip=1024 1073741824 bytes (1.1 GB) copied, 5.04356 s, 213 MB/s # dd if=/dev/mapper/VolGroup-lv_home of=/dev/null bs=1M count=1024 iflag=direct skip=1024 & dd if=/dev/mapper/VolGroup-lv_home of=/dev/null bs=1M count=1024 iflag=direct skip=2048 & dd if=/dev/mapper/VolGroup-lv_home of=/dev/null bs=1M count=1024 iflag=direct skip=3072 & dd if=/dev/mapper/VolGroup-lv_home of=/dev/null bs=1M count=1024 iflag=direct skip=4096 1073741824 bytes (1.1 GB) copied, 24.7348 s, 43.4 MB/s 1073741824 bytes (1.1 GB) copied, 24.7378 s, 43.4 MB/s 1073741824 bytes (1.1 GB) copied, 24.7408 s, 43.4 MB/s 1073741824 bytes (1.1 GB) copied, 24.744 s, 43.4 MB/s dd write test: one process and then four simultaneous processes # dd if=/dev/zero of=test bs=1M count=1024 oflag=direct 1073741824 bytes (1.1 GB) copied, 10.415 s, 103 MB/s # dd if=/dev/zero of=test bs=1M count=1024 oflag=direct & dd if=/dev/zero of=test2 bs=1M count=1024 oflag=direct & dd if=/dev/zero of=test3 bs=1M count=1024 oflag=direct & dd if=/dev/zero of=test4 bs=1M count=1024 oflag=direct 1073741824 bytes (1.1 GB) copied, 49.8874 s, 21.5 MB/s 1073741824 bytes (1.1 GB) copied, 49.8608 s, 21.5 MB/s 1073741824 bytes (1.1 GB) copied, 49.8693 s, 21.5 MB/s 1073741824 bytes (1.1 GB) copied, 49.9427 s, 21.5 MB/s I wonder is that normal situation or did I missed something?

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