Recently people started to ask me how to use Xdebug to figure out which parts of applications use a lot of memory. Traditionally this was part of Xdebug's profiling functionality. Unfortunately the cachegrind format didn't fit this so well, and because it returned incorrect data I removed this functionality from the profiler. However, there is other functionality in Xdebug that does provide the correct data: the function traces.

Function traces log every include, function call and method call to a file. If the xdebug.trace_format setting is set to "1" then the trace file is an easy-to-parse tab separated format. The information that is logged includes the time-index when the function started and ended, and it also contains the amount of memory that was in use when entering the function, as well as when leaving it. With the last two numbers it's rather trivial to write a script to figure out which functions/methods increase the memory usage a lot. Of course, nobody had written a script yet to do anything with this information

As part of my preparations for my Xdebug talk at IPC next week, I now have written such a script. The script parses the tab-separated function trace files and aggregates all the information by function name. You can sort the output on a few different keys: time-own, memory-own, time-inclusive, memory-inclusive and calls. You can also configure how many elements it will show. As an example here is some output from a trace of one of the presentation system's PHP scripts:

$ php tracefile-analyser.php trace.2043925204.xt memory-own 20

parsing...
Done.
Showing the 20 most costly calls sorted by 'memory-own'.
                                               Inclusive        Own
function                               #calls  time     memory  time     memory
-------------------------------------------------------------------------------
require_once                                9  0.0541  4595160  0.0277  2548104
{main}                                      1  0.0600  2906032  0.0034   249744
fread                                       4  0.0001    33296  0.0001    33296
session_start                               1  0.0002    31824  0.0002    31824
XML_Presentation->startHandler             38  0.0073    36360  0.0035    18424
_pres_slide->_pres_slide                   27  0.0009    10152  0.0009    10152
_presentation->_presentation                1  0.0001     7912  0.0001     7912
strtolower                                 67  0.0017     6456  0.0017     6456
compact                                     1  0.0000     4832  0.0000     4832
each                                        5  0.0001     4320  0.0001     4320
XML_Presentation->endHandler               38  0.0014     3800  0.0014     3960
_slide->_slide                              1  0.0001     3896  0.0001     3896
XML_Slide->startHandler                     4  0.0009    10800  0.0004     3736
_image->_image                              1  0.0000     3040  0.0000     3040
fopen                                       2  0.0001     2816  0.0001     2816
getimagesize                                1  0.0001     2296  0.0001     2296
display->display                            1  0.0001     2120  0.0001     2120
explode                                     2  0.0001     2120  0.0001     2120
xml_parser_create                           2  0.0001     1680  0.0001     1680
XML_Parser->_initHandlers                   2  0.0011     1600  0.0005     1360

The script is available in Xdebug's download package or at https://github.com/derickr/xdebug/raw/master/contrib/tracefile-analyser.php

The script to run is then "tracefile-analyser.php" from inside the "xdebug/contrib" directory.

Update 2009-12-28: Changed the CVS instructions to the new SVN instructions.

Update 2012-03-13: Changed the SVN instructions to a link to github.

svn co svn://svn.xdebug.org/svn/xdebug/xdebug/trunk/contrib