Comments on: Query Profiling with MySQL: Bypassing caches http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/ Everything about MySQL Performance Sat, 21 Nov 2009 05:23:57 -0800 http://wordpress.org/?v=2.8.4 hourly 1 By: Jonathon Hill » Speed-testing a query? Flush your MySQL caches http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/comment-page-1/#comment-619687 Jonathon Hill » Speed-testing a query? Flush your MySQL caches Wed, 29 Jul 2009 03:40:28 +0000 http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/#comment-619687 [...] to the MySQL Performance Blog for this [...] [...] to the MySQL Performance Blog for this [...]

]]> By: peter http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/comment-page-1/#comment-392675 peter Wed, 26 Nov 2008 18:19:42 +0000 http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/#comment-392675 JM, Think about it practically - DBMS works through OS using its caches. To get query uncached you need to clean these caches. for MyISAM you can do SET GLOBAL key_buffer_size=0 and when set it back to default. You can also do cat 3 > /proc/sys/vm/drop_caches on Linux to clear caches however you do not have anything for Innodb. In practice however fully empty case is not that interesting because query is likely to have something cached, dictionary information etc. I would have Slow Query log enabled with Percona Patches so you can see how many IOs query does etc. When query optimization usually can happen analytical way - if you see from EXPLAIN query scans 1000000 rows you do not need it to be IO bound to optimize it you can just estimate how it would be :) JM,

Think about it practically – DBMS works through OS using its caches. To get query uncached you need to clean these caches. for MyISAM you can do SET GLOBAL key_buffer_size=0 and when set it back to default. You can also do cat 3 > /proc/sys/vm/drop_caches on Linux to clear caches however you do not have anything for Innodb.

In practice however fully empty case is not that interesting because query is likely to have something cached, dictionary information etc. I would have Slow Query log enabled with Percona Patches so you can see how many IOs query does etc. When query optimization usually can happen analytical way – if you see from EXPLAIN query scans 1000000 rows you do not need it to be IO bound to optimize it you can just estimate how it would be :)

]]> By: JM http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/comment-page-1/#comment-392594 JM Wed, 26 Nov 2008 15:25:44 +0000 http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/#comment-392594 I have a web app which doesn't have a very large client base but each user can potentially query a large chunk of data. So the most important thing is when the user queries a given chunk the first time. Once it's cached it's of course orders of magnitude faster, but it's the initial query that I need to optimize. I imagined that having the ability to profile a query should be pretty basic in a rdbms. I have a web app which doesn’t have a very large client base but each user can potentially query a large chunk of data. So the most important thing is when the user queries a given chunk the first time. Once it’s cached it’s of course orders of magnitude faster, but it’s the initial query that I need to optimize. I imagined that having the ability to profile a query should be pretty basic in a rdbms.

]]> By: peter http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/comment-page-1/#comment-391758 peter Tue, 25 Nov 2008 19:04:23 +0000 http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/#comment-391758 ... In the same sense as with any other database. Practically everything has caches. To do real profiling you need to profile real query mix which will have each query having appropriate cache/hit ratio not running one query in the loop and assuming results will be fine. … In the same sense as with any other database. Practically everything has caches.

To do real profiling you need to profile real query mix which will have each query having appropriate cache/hit ratio not running one query in the loop and assuming results will be fine.

]]> By: JM http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/comment-page-1/#comment-391747 JM Tue, 25 Nov 2008 18:08:04 +0000 http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/#comment-391747 So does that mean that there is no way to profile a query in mysql? I can't be expected to reboot my system every time I want to tweak a query and test if it runs faster! So does that mean that there is no way to profile a query in mysql? I can’t be expected to reboot my system every time I want to tweak a query and test if it runs faster!

]]> By: Pythian Group Blog » Log Buffer #62: a Carnival of the Vanities for DBAs http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/comment-page-1/#comment-167687 Pythian Group Blog » Log Buffer #62: a Carnival of the Vanities for DBAs Fri, 14 Sep 2007 17:08:07 +0000 http://www.mysqlperformanceblog.com/2007/09/12/query-profiling-with-mysql-bypassing-caches/#comment-167687 [...] MySQL Performance Blog likewise offers some tips on bypassing caches at various system [...] [...] MySQL Performance Blog likewise offers some tips on bypassing caches at various system [...]

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