alestic/ec2-consistent-snapshot — pull request #39 by danielbeardsley (2014-07-09 22:39:49+00:00)
Title: Mysql: kill query on timeout

We have an SQL timeout, but it wasn't actually killing the query when
it times out. This is problem when issuing the FLUSH TABLES command
because it occasionally locks up the database if there is a
long-running write query.

Now, we kill the query when the timeout hits which also kills it upon
CTRL-C'ing

See here for the problem (fixes #23):
https://github.com/alestic/ec2-consistent-snapshot/issues/23

Got the idea for the fix from here:
http://www.perlmonks.org/?node_id=885620

I've tested the following:

1. Call: sql_timeout_retry("SELECT SLEEP(60);", 0.5, 10, 5); after
connecting.
2. Check the processlist while this is happening:
Before: We see the query in the list all the time because the
timeout *doesn't* stop the query
After: query is rarely seen in the list cause it times out and is
killed after 0.5s
3. Interrupt the process (Ctrl-C) while it's happening
Before: Query is still in the processlist until it finishes
After: Query is killed when the process is killed.