MySQL - can I limit the maximum time allowed for a query to run?

Question

I'm looking for a way to limit the max running time of a query on mysql server. I figured this could be done through the my.cnf configuration file, but couldn't find anything relevant in the docs. Anyone knows if this could be done? thanks.

Answer 1

There is no way to specify a maximum run time when sending a query to the server to run.

However, it is not uncommon to have a cron job that runs every second on your database server, connecting and doing something like this:

1. SHOW PROCESSLIST
2. Find all connections with a query time larger than your maximum desired time
3. Run KILL [process id] for each of those processes

Answer 2

You could use a query as follows:

SELECT MAX_STATEMENT_TIME=1000 * FROM table;

UPDATE: You should use max_execution_time instead.

SELECT /*+ MAX_EXECUTION_TIME(1000)*/ * FROM table;

MAX_STATEMENT_TIME was renamed to max_execution_time in MySQL 5.7.8. http://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_max_execution_time

Answer 3

In the meantime the Twitter team released their changes to MySQL which implements this:

- Reduce unnecessary work through improved server-side statement timeout support. This allows the server to proactively cancel queries that run longer than a millisecond-granularity timeout.

See http://engineering.twitter.com/2012/04/mysql-at-twitter.html and https://github.com/twitter/mysql/wiki/Statement-Timeout

Answer 4

http://mysqlserverteam.com/server-side-select-statement-timeouts/

Interesting upgrade. I will check it:

"MySQL 5.7.4 introduces the ability to set server side execution time limits, specified in milliseconds, for top level read-only SELECT statements".

SET GLOBAL MAX_STATEMENT_TIME=1000;
SET SESSION MAX_STATEMENT_TIME=2000;
SELECT MAX_STATEMENT_TIME=1000 * FROM table;