…What cache hit rate is good for optimal MySQL Performance” is typical question I’m asked. It could by … good was OS or SAN cache hit rate – something you would not see otherwise. The bad luck is – MySQL currently does not provide this… do. For example if single query is issuing 100+ random IO requests which are not cached by OS or SAN this is…
Post: MySQL Query Cache
July 27, 2006 By 69 Comments
…MySQL Query Cache is – I’ve seen number of people being confused, thinking MySQL Query Cache is the same as Oracle Query Cache – meaning cache where execution plans are cached. MySQL Query Cache…
Post: Beware large Query_Cache sizes
March 23, 2007 By 3 Comments
… had number of consulting projects with MySQL Query Cache being source of serious problems. One would see queries both for MyISAM and Innodb tables… invalidations to happen more regularly but this also should affect query cache hit rate.
Post: Beyond great cache hit ratio
May 19, 2010 By 2 Comments
… gets (hits) to retrieve some data plus there are 10 more requests which resulted in misses and caused MySQL queries. The hit ratio is… single object. You have 1 request (hit) now and 10 misses which drops your hit rate down to less than 10% but performance… get best hit rate. Others which have hundreds of page views per user per session may be good enough with caches which are…
Post: Why you should ignore MySQL's key cache hit ratio
February 28, 2010 By 27 Comments
…99% of advice about tuning MySQL‘s key cache hit ratio is wrong, even …cache interchangeably. However, I will be careful about the difference between “rate” and “ratio”. In this article, the key cache miss rate…hit ratio the user desires by running silly queries that do nothing but cause buffer hits…
Post: MySQL caching methods and tips
April 4, 2011 By 4 Comments
… same time. These cache stampedes are essentially the cause of the unpredictable performance of the MySQL query cache, since the rate of invalidation can not be controlled, and multiple cache entries may be invalidated by… run when the cache is empty. When talking about cache, the miss path is at least as important as the hit one. In…
Post: Using flow control functions for performance monitoring queries
May 24, 2008 By 12 Comments
… like IF or CASE used in MySQL Queries as they are often abused used to create queries which are poorly readable as well as can hardly be optimized well by MySQL Optimizer. One way… cache (or be served from the cache all together). Bots however tend to visit distinct pages which tends to have significantly lower cache hit rate…
Comment: MySQL Query Cache
August 13, 2009 By 69 Comments
…% Cache hit rate does it mean it is not worth it ? Not really it depends on which queries are cached, as well as overhead query cache provides… in High performance MySQL Server book, in their its said “What’s a good cache hit rate? It depends. Even a 30% hit rate can be very helpful, because the work saved by not executing queries is typically…
Comment: When should you store serialized objects in the database?
January 21, 2010 By 42 Comments
… to cache without any extra effort. We see a 99.9% cache hit rate in production. In practice, that means that even if the queries through to MySQL are somewhat slower, the machine is serving so many fewer queries that it’s hardly…
Comment: MyISAM mmap feature (5.1)
June 14, 2006 By 10 Comments
… my OS cache efficiency. I use munin and RRD to graph as many stats about MySQL as possible. Number of slow queries, query cache efficiency, etc. The problem is I can’t figure out where Linux keeps stats on its file cache hit rate. Anyone…
