Profiling memory usage

Original article is here, follow that for most of the process: http://derickrethans.nl/xdebug_and_tracing_memory_usage.php

Alternatively you can get the tracefile-analyser.php file from xdebug/xdebug github repo. 

This below settings in only applicable if you are using xdebug v2.*

zend_extension="/usr/lib/php5/20060613/xdebug.so"
xdebug.profiler_enable_trigger = on
xdebug.profiler_output_dir = /home/catch/www/cachegrind
xdebug.remote_enable = 1
xdebug.remote_port = 9000
xdebug.remote_host = localhost
xdebug.profiler_output_name = cachegrind.out.%R
xdebug.profiler_append = TRUE
xdebug.auto_trace = 1
xdebug.trace_format = 1

If you are using xdebug v3.* or above then use the below settings.

xdebug.client_host=localhost # host.docker.internal if you are using ddev.
xdebug.client_port=9003
xdebug.start_with_request=yes
xdebug.mode=trace
xdebug.output_dir=/var/www/html/xdebug-profiler
xdebug.trace_output_name=trace.%R.out
xdebug.trace_format=1

Please note the following settings has been removed or renamed in xdebu V3.*.

When you run the script sorting by 'memory own' - i.e. how much memory each function consumes, you'll get a table like this:

Showing the 30 most costly calls sorted by 'memory-own'.

                                               Inclusive        Own
function                               #calls  time     memory  time     memory
-------------------------------------------------------------------------------
drupal_load                                37  0.0140   799248  0.0055   535792
_registry_check_code                        7  0.0032   475792  0.0010   321200
_drupal_bootstrap_full                      1  0.0414  1721632  0.0016   303904
has_krumo                                   1  0.0038   301152  0.0033   300848
drupal_bootstrap                            3  0.0717  3154272  0.0012   295224
_drupal_bootstrap_database                  1  0.0006   258424  0.0005   248528
module_load_include                         7  0.0024   196928  0.0012   194248
require_once                               31  0.0055   437816  0.0026   114032
unserialize                                 8  0.0004    86696  0.0004    86696
Database::openConnection                    1  0.0012    80344  0.0003    73944
system_list                                 3  0.0092    64296  0.0016    51344
ob_start                                    1  0.0000    41016  0.0000    41016
drupal_static                              63  0.0041    31560  0.0028    31560
require                                     4  0.0007   149464  0.0002    19848
module_implements                           8  0.0032    86808  0.0006    13824
PDOStatement->fetchObject                   6  0.0002    10760  0.0002    10760
PDOStatement->execute                      11  0.0056    10592  0.0056    10592
include_once                               34  0.0066   212480  0.0024    10344
module_list                                 4  0.0097    74128  0.0002     9560
_drupal_bootstrap_variables                 1  0.0058   131056  0.0002     8552
_drupal_bootstrap_page_cache                1  0.0088   402848  0.0003     8496
variable_get                               39  0.0009     8320  0.0009     8320
drupal_get_filename                        85  0.0039     7408  0.0029     7408
PDO->prepare                                7  0.0008     6784  0.0003     5920
MergeQuery_mysql->__toString                1  0.0002     7552  0.0001     5744
drupal_environment_initialize               1  0.0005     7312  0.0002     5416
DatabaseConnection->prefixTables           11  0.0011    10304  0.0006     5248
define                                    174  0.0035     5200  0.0035     5200
strtr                                      11  0.0003     5056  0.0003     5056
drupal_settings_initialize                  1  0.0018    12600  0.0004     4784

I've also attached a patch to xdebug/api which makes it work on PHP5.2 - only works with memory-own sorting, but that's good enough for our purposes.