May 30, 2017

[HDGEM] The MySQL query cache is a query results cache.

The MySQL query cache compares incoming queries that start with SEL to a hash table, and if there is a match returns the results from the previous execution of the query. There are some restrictions:

The query must match byte-for-byte (the query cache avoids parsing)
Use of non-deterministic features will result in the query not being cached (including temporary tables, user variables, RAND(), NOW() and UDFs.)
The query cache was designed to not serve stale results.  Any modification to the underlying table(s) results in all cache being invalidated for those tables.
There are some restrictions on if the cache can be used for InnoDB (to respect MVCC; as you have a transaction open, the 'cache' might not represent the data in your expected view.)


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Posted By Blogger to HDGEM at 5/30/2017 12:21:00 PM