Finding memory leaks in PHP objects

I recently spent quite some time figuring out why a (cli) php script was eating all the memory. In PHP, memory leaks mostly show up in long running scripts. In my case, it was doing calculations on (a lot of) database records.

The script crashed all the time, because it was running against the memory_limit. After trying to figure out what was going wrong (using Xdebug’s function traces, PHP’s garbage collection, the unset trick of Paul M. Jones, etc…), I turned to a simple but effective manner to inspect the (problem) object.

Write your object to a file from time to time, and diff it.

Dumping your object:

    '/tmp/myobject_' . time() . '.txt',
    print_r($object, true)

// do other logic

    '/tmp/myobject_' . time() . '.txt',
    print_r($object, true)

Now you can see how big your object is getting (just by watching the filesize):

$ ls -al /tmp/myobject_*

And now you can pick two files to actually see what is causing the problem:

$ diff /tmp/myobject_1357140320.txt /tmp/myobject_1357140450.txt
>             [931277dc8ecbbb394b7f5454f64c5d0c] => Array
>                 (
>                     [hash] => 4143484432
>                     [mtime] => 1357137505
>                     [expire] => 1357141105
>                     [tags] => Array
>                         (
>                         )
>                 )

In my case Zend_Db_Profiler was enabled and was keeping track of all the queries in memory.

  • Dane Lowe