Comments on: Beware large Query_Cache sizes http://www.mysqlperformanceblog.com/2007/03/23/beware-large-query_cache-sizes/ Everything about MySQL Performance Thu, 28 Aug 2008 00:02:53 +0000 http://wordpress.org/?v=2.5.1 By: James Day http://www.mysqlperformanceblog.com/2007/03/23/beware-large-query_cache-sizes/#comment-95327 James Day Sun, 25 Mar 2007 23:59:45 +0000 http://www.mysqlperformanceblog.com/2007/03/23/beware-large-query_cache-sizes/#comment-95327 http://bugs.mysql.com/bug.php?id=21074 is worth watching, since it is about improvement of the time to insert the freed query cache record into the sorted list of free blocks. Flush query cache defragments the query cache, so regular flushing is one possible way of reducing the impact. On a related topic, http://bugs.mysql.com/bug.php?id=21051 has improved the reset query cache operation and caused it to be less likely to block other queries in 5.0.25 and 5.1.12 and later. A reset might be less painful than a flush before a rare table update, even though it'll remove all of the cached queries. The query cache design will undoubtedly be improved to better suit large cache sizes at some time. For the moment, it's intended for fairly small cache sizes, in tens rather than hundreds of megabytes. http://bugs.mysql.com/bug.php?id=21074 is worth watching, since it is about improvement of the time to insert the freed query cache record into the sorted list of free blocks. Flush query cache defragments the query cache, so regular flushing is one possible way of reducing the impact.

On a related topic, http://bugs.mysql.com/bug.php?id=21051 has improved the reset query cache operation and caused it to be less likely to block other queries in 5.0.25 and 5.1.12 and later. A reset might be less painful than a flush before a rare table update, even though it’ll remove all of the cached queries.

The query cache design will undoubtedly be improved to better suit large cache sizes at some time. For the moment, it’s intended for fairly small cache sizes, in tens rather than hundreds of megabytes.

]]> By: peter http://www.mysqlperformanceblog.com/2007/03/23/beware-large-query_cache-sizes/#comment-94825 peter Sun, 25 Mar 2007 10:47:36 +0000 http://www.mysqlperformanceblog.com/2007/03/23/beware-large-query_cache-sizes/#comment-94825 Could be. However in this case I do not see why single update would invalidate a lot of queries. As far as I know they have millions of tables so updating each of them should invalidate only few. The problems with extreme number of tables is another story. Could be. However in this case I do not see why single update would invalidate a lot of queries.
As far as I know they have millions of tables so updating each of them should invalidate only few.

The problems with extreme number of tables is another story.

]]> By: Kevin Burton http://www.mysqlperformanceblog.com/2007/03/23/beware-large-query_cache-sizes/#comment-93438 Kevin Burton Fri, 23 Mar 2007 22:01:07 +0000 http://www.mysqlperformanceblog.com/2007/03/23/beware-large-query_cache-sizes/#comment-93438 Yeah.. I think Wordpress.com had this problem for a while as well. Yeah.. I think Wordpress.com had this problem for a while as well.

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