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.

Kamerman

possible duplicate of How to set a maximum execution time for a mysql query ? – Charlatanism

this points to a lock_wait_timeout, which is not what I need. I want an expiration timeout on the query, regardless if a lock was acquired or not. – Kamerman

Answer 1

Update

As of MySQL 5.7, you can include a MAX_EXECUTION_TIME optimizer hint in your SELECT queries to instruct the server to terminate it after the specified time.

As far as I know, if you want to enforce a server-wide timeout, or if you care about queries besides SELECTs, the original answer is still your only option.

Original answer

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

Foucault

every second may be a bit of overkill depending on your situation. You should put some thought into the need to kill processes in order to keep your max_connections from being hit - all this depends on the load on your specific machine. – Schriever

This is no longer true. Please see the posts about using max_execution_time. – Jaymie

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

Conceit

Try to improve your answer – Fisch

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

Passerby

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;

Tinsmith