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PHP : Function Reference : Advanced PHP debugger

Advanced PHP debugger


APD is the Advanced PHP Debugger. It was written to provide profiling and debugging capabilities for PHP code, as well as to provide the ability to print out a full stack backtrace. APD supports interactive debugging, but by default it writes data to trace files. It also offers event based logging so that varying levels of information (including function calls, arguments passed, timings, etc.) can be turned on or off for individual scripts.


APD is a Zend Extension, modifying the way the internals of PHP handle function calls, and thus may or may not be compatible with other Zend Extensions (for example Zend Optimizer).


APD is currently available as a PECL extension from » Make sure you have installed the CGI version of PHP and it is available in your current path along with the phpize script.

Run the following command to download, build, and install the latest stable version of APD:

pear install apd

This automatically installs the APD Zend module into your PHP extensions directory. It is not mandatory to keep it there; you can store the module in any directory PHP can read as long as you set the zend_extension parameter accordingly.

Windows users can download the extension dll php_apd.dll from »

In your INI file, add the following lines:

zend_extension = /absolute/path/to/
apd.dumpdir = /absolute/path/to/trace/directory
apd.statement_tracing = 0

Depending on your PHP build, the zend_extension directive can be one of the following:

zend_extension              (non ZTS, non debug build)
zend_extension_ts           (    ZTS, non debug build)
zend_extension_debug        (non ZTS,     debug build)
zend_extension_debug_ts     (    ZTS,     debug build)

Building on Win32

To build APD under Windows you need a working PHP compilation environment as described on -- basically, it requires you to have Microsoft Visual C++,, bison/flex, and some know how to get it to work. Also ensure that adp.dsp has DOS line endings; if it has unix line endings, Microsoft Visual C++ will complain about it.

Runtime Configuration

The behaviour of these functions is affected by settings in php.ini.

Table 19. APD Configuration Options

Name Default Changeable Changelog
apd.dumpdir NULL PHP_INI_ALL  
apd.statement_tracing "0" PHP_INI_ALL Available since apd 0.9.

For further details and definitions of the PHP_INI_* constants, see the Appendix I, php.ini directives.

Here's a short explanation of the configuration directives.

apd.dumpdir string

Sets the directory in which APD writes profile dump files. You can specify an absolute path or a relative path.

You can specify a different directory as an argument to apd_set_pprof_trace().

apd.statement_tracing boolean

Specfies whether or not to do per-line tracings. Turning this on (1) will impact the performance of your application.

Resource Types

This extension has no resource types defined.

Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

Table 20. APD constants

Constant Value Description
FUNCTION_TRACE (integer) 1  
ARGS_TRACE (integer) 2  
ASSIGNMENT_TRACE (integer) 4  
STATEMENT_TRACE (integer) 8  
MEMORY_TRACE (integer) 16  
TIMING_TRACE (integer) 32  
SUMMARY_TRACE (integer) 64  
ERROR_TRACE (integer) 128  
PROF_TRACE (integer) 256  
APD_VERSION (string) example: 1.0.2-dev  

How to use PHP-APD in your scripts

  1. As the first line of your PHP script, call the apd_set_pprof_trace() function to start the trace:

    apd_set_pprof_trace(); ?>

    You can insert the line anywhere in your script, but if you do not start tracing at the beginning of your script you discard profile data that might otherwise lead you to a performance bottleneck.

  2. Now run your script. The dump output will be written to apd.dumpdir/pprof_pid.ext.


    If you're running the CGI version of PHP, you will need to add the '-e' flag to enable extended information for apd to work properly. For example: php -e -f script.php

  3. To display formatted profile data, issue the pprofp command with the sort and display options of your choice. The formatted output will look something like:

    bash-2.05b$ pprofp -R /tmp/pprof.22141.0

    Trace for /home/dan/testapd.php
    Total Elapsed Time = 0.00
    Total System Time  = 0.00
    Total User Time    = 0.00

    Real         User        System             secs/    cumm
    %Time (excl/cumm)  (excl/cumm)  (excl/cumm) Calls    call    s/call  Memory Usage Name
    100.0 0.00 0.00  0.00 0.00  0.00 0.00     1  0.0000   0.0009            0 main
    56.9 0.00 0.00  0.00 0.00  0.00 0.00     1  0.0005   0.0005            0 apd_set_pprof_trace
    28.0 0.00 0.00  0.00 0.00  0.00 0.00    10  0.0000   0.0000            0 preg_replace
    14.3 0.00 0.00  0.00 0.00  0.00 0.00    10  0.0000   0.0000            0 str_replace

    The -R option used in this example sorts the profile table by the amount of real time the script spent executing a given function. The "cumm call" column reveals how many times each function was called, and the "s/call" column reveals how many seconds each call to the function required, on average.

  4. To generate a calltree file that you can import into the KCacheGrind profile analysis application, issue the pprof2calltree comand.

Contact information

If you have comments, bugfixes, enhancements or want to help developing this beast, you can send an mail to » Any help is very welcome.

Table of Contents

apd_breakpoint — Stops the interpreter and waits on a CR from the socket
apd_callstack — Returns the current call stack as an array
apd_clunk — Throw a warning and a callstack
apd_continue — Restarts the interpreter
apd_croak — Throw an error, a callstack and then exit
apd_dump_function_table — Outputs the current function table
apd_dump_persistent_resources — Return all persistent resources as an array
apd_dump_regular_resources — Return all current regular resources as an array
apd_echo — Echo to the debugging socket
apd_get_active_symbols — Get an array of the current variables names in the local scope
apd_set_pprof_trace — Starts the session debugging
apd_set_session_trace — Starts the session debugging
apd_set_session — Changes or sets the current debugging level
apd_set_socket_session_trace — Starts the remote session debugging
override_function — Overrides built-in functions
rename_function — Renames orig_name to new_name in the global function table

Code Examples / Notes » ref.apd


Some useful links on APD:
1. Profiling PHP Applications ( ), [1.40 MB], George Schlossnagle, 2004-09-23
2. PHP Performance Profiling ( ), [13.16 KB], Jonathan Oxer, 2003-10-21
3. APD Wiki ( )
R. Rajesh Jeba Anbiah


re: iainargent at hotmail dot com
i've been able to run pecl install apd against PHP 5.2.4 without any issues, although you are right, development seems to have completely ceased


Locate the root-cause of defects, fast.
If you need to locate the source of a defect in complicated web-based PHP applications with lots of conditional includes (osCommerce and Zen-Cart are reasonably complex), use APD to create a profile dump.
Then filter the dump for lines containing "!" to produce a list of included (required) files in the order they were included.
On my Win98 dev box I use: find "!" dumpfile > trace_program.txt
I use the trace_program.txt to backtrack to the root-cause of defects appearing in the browser.  Great for maintaining systems you did not build yourself.

judas dot iscariote

if you are looking for better/different alternatives to APD, check the xdebug website or download it from PECL


If pprofp reports 'No such file or directory', it's probably because it contains an incorrect path to your php client. Open pprofp in your fav editor, edit the first line, and try again.


Development seems to have ceased on this project. It doesn't work with PHP 5.2 and this bug has been open for nearly a year now.

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