MySQL Bugs: #34880: Warnings are shown on assigning valid values to variable query_cache

Bug #34880	Warnings are shown on assigning valid values to variable query_cache_size
Submitted:	27 Feb 2008 11:05	Modified:	12 Jun 2008 16:36
Reporter:	Salman Rawala	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Documentation	Severity:	S3 (Non-critical)
Version:		OS:	Any
Assigned to:	Paul DuBois	CPU Architecture:	Any
Tags:	query_cache_size

Description:
When we assign any valid value to variable, a warning message appears "Query cache failed to set size 1024; new query cache size is 0". 

How to repeat:
Sample Code: 
SET @@global.query_cache_size = 1024;

Actual Output:
SET @@global.query_cache_size = 1024;
Warnings:
Warning	1282	Query cache failed to set size 1024; new query cache size is 0
SELECT @@global.query_cache_size;
@@global.query_cache_size
0

Thank you for a problem report. I think, manual should be more clear about possible values of variables that defines query cache (both default and relative to each other). 

This pages:

http://dev.mysql.com/doc/refman/5.0/en/server-system-variables.html
http://dev.mysql.com/doc/refman/5.1/en/server-system-variables.html

should be fixed.

http://dev.mysql.com/doc/refman/5.0/en/query-cache-configuration.html

"
When you set query_cache_size to a non-zero value, keep in mind that the query cache needs a minimum size of about 40KB to allocate its structures.  (The exact size depends on system architecture.) If you set the value too small, you'll get a warning
"

Thank you for your bug report. This issue has been addressed in the documentation. The updated documentation will appear on our website shortly, and will be included in the next release of the relevant products.

Added a note to the query_cache_size description.