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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.

sa125
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    possible duplicate of [How to set a maximum execution time for a mysql query ?](http://stackoverflow.com/questions/415905/how-to-set-a-maximum-execution-time-for-a-mysql-query) – miku Jan 25 '11 at 14:43
  • 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. – sa125 Jan 25 '11 at 14:51

4 Answers4

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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
TehShrike
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    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. – Ross Jun 10 '13 at 12:38
  • This is no longer true. Please see the posts about using `max_execution_time`. – nlta Jul 22 '21 at 04:10
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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

Alexander Kosolapov
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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

faker
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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;
Grenville Tryon
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