Have PHP dump heap on OutOfMemory exception

I am currently debugging a script that constantly runs into OutOfMemory exceptions. It is run as a cronjob and usually runs fine, but when the cronjob wasn't run for a while (for whatever reason) the script has to handle to many elements that queued up and will run into a OutOfMemory exception.

From examining the code I was not able to spot the problem. I believe one of the iterative function calls might leak memory, but I am not sure which one and where. Is there an 开发者_运维技巧option to get PHP to dump the heap, when an OutOfMemory exception occurs? I might be able to spot the problem from there (most likely).

While I was not able to find a "dump heap on Exception" option, I did find get_defined_vars() which is basically a heap dump if called from a global scope. Using this I was able to see that there where hundreds (actually thousands) of still referenced database rows hanging around in my memory. This was due to a not freed mysql result resource somewhere in the infamous function that caused the leak. I found it and fixed it. It runs well now.

Well, easiest approach would be to use a try-catch block around that part of your script where the error possibly occurs and you will have to dump the stack in the catch part. The problem might be that the machine won't be able to react cause the memory is full and it terminates. I do not know if it helps to discard some variables to free up some memory to output some data.

EDIT: For this purpose use the php function debug-backtrace. This will give you a stack trace. So finding the error will be much likely in case the machine is still up.

Just do not load all objects together to memory, but read-as-you-process-them?

I've had lots of problems with simpleXML and memory leaks. They are a pain in the are to track down... took me days to figure out that simpleXML was causing then and then fix them. As far as i know you cand programatically set a handled for OOM:)

Also, PHP's functions for displaying memory info fails to detect the memory leaks, i had scripts eating up ~1Gb of ram, but PHP's functions reported only 100Mb used:)

This is as good of a 'heap dump' as I'm able to quickly write in PHP. I take the defined variables and functions, then sort by their serialized length. Serialized length isn't a 100% reliable method for getting a variable's size, but it's pretty good, and generally useful for determining which objects are your memory hogs:

$memmap = array_map(function($var) { return strlen(serialize($var)); }, array_merge(get_defined_functions(), get_defined_vars())); arsort($memmap); var_dump($memmap);

You may want to tweak the callback function a bit if you'd like your results to be more verbose, or to recurse through the defined variables.

I've never seen PHP provide a native facility for this but a few other things might exist:

Try: https://github.com/mcfunley/php-heap/blob/master/php-heap.py

It could also be possible to write an extension to achieve the same.