Bug #79170 mysqldump: (single-transaction + flush-log) flush the query cache
Submitted: 7 Nov 2015 23:37 Modified: 14 Nov 2019 3:21
Reporter: Raphaël Droz Email Updates:
Status: Not a Bug Impact on me:
None 
Category:MySQL Server: mysqldump Command-line Client Severity:S3 (Non-critical)
Version:5.5 OS:Any
Assigned to: MySQL Verification Team CPU Architecture:Any

[7 Nov 2015 23:37] Raphaël Droz 
Description:
Although undocumented combining
single-transaction and flush-log parameters to mysqldump issues a query-cache flush which is normally not expected.

Both options are useful and may be used routinely, even every few X hours where a query cache flush is an undesirable side-effect.

It should either be fixed or, at the very least, documented.

How to repeat:
$ sudo mysqldump --defaults-file=/etc/mysql/debian.cnf --single-transaction --flush-logs --no-data mysql user
$ mysql -Ne "SHOW STATUS LIKE 'Qcache_free_memory'"
<value get back the original maximal free memory>
[7 Nov 2015 23:40] Raphaël Droz 
Also reported here a two years ago:
http://forums.mysql.com/read.php?28,592024,592024
[14 Nov 2019 3:21] MySQL Verification Team 
This is not a bug but intentional behavior. Also, query cache is retired.