MySQL Bugs: #11870: Include QUERY CACHE information in EXPLAIN output

Bug #11870	Include QUERY CACHE information in EXPLAIN output
Submitted:	11 Jul 2005 20:43	Modified:	7 Jul 2017 9:14
Reporter:	Kolbe Kegel	Email Updates:
Status:	Won't fix	Impact on me:	None
Category:	MySQL Server: Query Cache	Severity:	S4 (Feature request)
Version:		OS:	Any
Assigned to:		CPU Architecture:	Any

Description:
The output of EXPLAIN, or an alternative command, should show information about whether the result of a query will be stored in the Query Cache.

How to repeat:
n/a

Suggested fix:
The information provided could include whether or not the query is cacheable, and if not it could give the reason (ie. refers to UDF, refers to user-defined variable, refers to non-idempotent function, etc). It could also be shown whether the query is already in the cache and how much space the result for the query uses in the query cache.

Possible implementations include an additional column of output in EXPLAIN, which could either be automatically included or triggered by EXPLAIN SQL_CACHE SELECT or some other syntax. Another possibility is to show this output only if it is asked for explicitly, and to show the output independent of any other output.

bug 23714 is a source of information about cache size

MySQL will no longer invest in the query cache, see:

http://mysqlserverteam.com/mysql-8-0-retiring-support-for-the-query-cache/