Bottomless, Endless

When doing statistical computations on a DB, you can easily reach the default memory and execution time limits of PHP.

You could change those settings directly in your php.ini file, but it would make the changes server-wide, meaning that even those scripts that should never eat that much memory can potentially hog the system if they start running wild.
It’s better to enable it on a file basis, if not on a compute-heavy function basis using ini_set.

For instance if your script reaches the default 16M of memory usage, this message will appear:

PHP error: Fatal error: Allowed memory size of 16777216 bytes exhausted

To change the default value:

ini_set('memory_limit', '20M');

When reaching the maximum execution time of a script you’ll get this message:

Maximum execution time of 30 seconds exceeded

To change the default value:

ini_set('max_execution_time', 90);

When dealing with extremely long processes, like for instance sending millions of notifications to your app users on Facebook, you might even want to use as much memory and time as possible:

ini_set('memory_limit','900M');
ini_set('max_execution_time', 90000);
ini_set('display_errors', 1);