Mysql caches: Difference between revisions
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Each cache entry knows which tables it references for permissions, and cache-invalidation.<br> | Each cache entry knows which tables it references for permissions, and cache-invalidation.<br> | ||
Whenever any row is changed in a table, all cache entries using that table are purged. | Whenever any row is changed in a table, all cache entries using that table are purged. | ||
<syntaxhighlight lang="mysql"> | |||
SHOW VARIABLES LIKE 'query_cache_size'; # if '0', query cache is disabled | |||
</syntaxhighlight> | |||
</blockquote><!-- The Query Cache --> | </blockquote><!-- The Query Cache --> | ||
Revision as of 02:04, 7 September 2022
Query Cache (<8.0)
NOTE:
It is disabled by default starting in MySQL-5.6
https://dev.mysql.com/blog-archive/mysql-8-0-retiring-support-for-the-query-cache/The query cache is a key-value store of cacheable-queries, and their result.
This interferes with benchmarking, since repeat queries may be much faster to lookup.To avoid the query cache:
# 1. Add a calculated-function to your selected rows - since they are not cacheable # TODO: validate SELECT ..., NOW() FROM ... # 2. Use 'SQL_NO_CACHE' in your query # (This often has not worked for me) SELECT SQL_NO_CACHE ... FROM ...It is implemented as an LRU key-value store for exact (byte-for-byte) query matches.
Each cache entry knows which tables it references for permissions, and cache-invalidation.
Whenever any row is changed in a table, all cache entries using that table are purged.SHOW VARIABLES LIKE 'query_cache_size'; # if '0', query cache is disabled
The OS Cache
TODO:
research