[DBAL-275] Automatically attempt to reconnect a dropped persistent MySQL-connection (MySQL server has gone away)

Wed, 21 Nov 2012 11:39:50 +0000

For php-scripts that run for a long time (a.o. daemons) persistent connections will almost always be dropped by the MySQL-server after a set timeout (depending on wait_timeout). This will have Doctrine throw an exception and have the php-script terminate if not catched. It is not practical to catch the same Exception with a try-catch around every query.

I have fixed this for DBAL 2.1.6 by adding a custom layer of Statement-, Connection- and Driver classes.
Key functionalities:

The custom layer will transparently catch dropped connections and attempt a number of times (configurable) to reconnect.
The behaviour will not be triggered in a transaction (in that case it will revert to throwing an exception just like before).
The reconnect behaviour is not MySQL specific per se. It can be triggered by any Exception for any Driver-type if a Driver provides a method 'getReconnectExceptions'.
Minimal performance-impact. Only when an Exception is thrown will it be searched for a matching Exception to possibly trigger the behaviour. (also the reason a single stringmatch is used)

Why this functionality?

It is often not possible to change settings of a database-server.
In a production environment the MySQL wait_timeout is often set to mere seconds
Doctrine's use of persistent connections will become a little more persistent
More reliable and robust php-scripts built on top of the DBAL

See files in attached archive to get an idea of the code. Enabling the layer is currently done like this (Symfony2 yml):
doctrine:
dbal:
wrapper_class: DoP\DoPBundle\Doctrine\DBAL\Connection
driver_class: DoP\DoPBundle\Doctrine\DBAL\Driver\PDOMySql\Driver
options:
x_reconnect_attempts: 2

Maybe I overlook something, but I only see pro's, no cons, to this improvement. I have created this issue to poll if you think this is a welcome feature and are interested to have me rework the code into DBAL itself? Reworking it into DBAL itself would certainly greatly reduce my code.

If agreed I'll create a github pull request when finished with the code and take comments/improvements from there.

(Also, I have glanced over http://www.doctrine-project.org/contribute.html but did not find any coding/testing-guidelines. Can you point me in the right direction?)

Regards,

Dieter

Doctrine Project

[DBAL-275] Automatically attempt to reconnect a dropped persistent MySQL-connection (MySQL server has gone away)