MEMINFO

PHP Meminfo is a PHP extension that gives you insights on the PHP memory content.

Its main goal is to help you understand memory leaks, but by looking at data present in memory, you can better understand your application behaviour.

One of the main source of inspiration for this tool is the Java jmap tool with the -histo option (see man jmap).

Compatibility

Compiled and tested on:

• PHP 5.4.4 (Debian 7)
• PHP 5.5.8 (Ubuntu 12.04 LTS)
• PHP 5.5.20 (CentOS 7)

Compilation instructions

You will need the phpize command. It can be installed on a Debian based system by:

$ apt-get install php5-dev

Once you have this command, follow this steps:

Compilation

From the root of the extension directory:

$ phpize
$ ./configure --enable-meminfo
$ make
$ make install

Enabling the extension

Add the following line to your php.ini:

extension=meminfo.so

Usage

All meminfo functions take a stream handle as a parameter. It allows you to specify a file, as well as to use standard output with the php://stdout stream.

Exploring Memory usage

The provided user interface allows you to explore the content of your memory. It will show you the items instanciated, the dependencies between items and the size of each of them.

Summary Screen

The main screen lists the top memory consumers, ordered by their total size.

Item details Screen

Clicking on an item brings you to the Item Details Screen.

On this screen, you will see 5 parts:

• title Item type (object, array, string, boolean, etc...) and its pointer address in memory at the time of the data extraction. This memory address is used as the unique identifier of the item

• Information Small summary on the item itself, like the class name in case of object and memory size information.

How memory size is computed

See the dedicated documentation.

Object instances count per class

Display the number of instances per class, ordered descending. Very useful to identify the content of a memory leak.

    meminfo_objects_summary(fopen('php://stdout','w'));

The result will provide something similar to the following example (generated at the end of the Symfony2 console launch)

    Instances count by class:
    num          #instances   class
    -----------------------------------------------------------------
    1            181          Symfony\Component\Console\Input\InputOption
    2            88           Symfony\Component\Console\Input\InputDefinition
    3            77           ReflectionObject
    4            46           Symfony\Component\Console\Input\InputArgument
    5            2            Symfony\Bridge\Monolog\Logger
    6            1            Symfony\Component\EventDispatcher\ContainerAwareEventDispatcher
    7            1            Doctrine\Bundle\MigrationsBundle\Command\MigrationsDiffDoctrineCommand
    ...

Note: It's a good idea to call the gc_collect_cycles() function before executing meminfo_objects_summary(), as it will collect dead objects that has not been reclaimed by the ref counter due to circular references. See http://www.php.net/manual/en/features.gc.php for more details.

Examples

The examples/ directory at the root of the repository contains more detailed examples.

    $ php examples/objects_summary.php

##List of currently active objects Provides a list of live objects with their class and their handle, as well as the total number of active objects and the total number of allocated object buckets.

    meminfo_objects_list(fopen('php://stdout','w'));

For example:

Objects list:
  - Class MyClassB, handle 2, refCount 1
  - Class MyClassC, handle 5, refCount 1
  - Class MyClassC, handle 6, refCount 1
  - Class MyClassC, handle 7, refcount 1
Total object buckets: 7. Current objects: 4.

Note: The same remark about gc_collect_cycle() before meminfo_objects_summary() applies as well for this function.

Examples

The examples/ directory at the root of the repository contains more detailed examples.

php examples/objects_list.php

Information on structs size

Display size in byte of main data structs size in PHP. Will mainly differ between 32bits et 64bits environments.

    meminfo_structs_size(fopen('php://stdout','w'));

It can be useful to understand difference in memory usage between two platforms.

Example Output on 64bits environment:

    Structs size on this platform:
      Class (zend_class_entry): 568 bytes.
      Object (zend_object): 32 bytes.
      Variable (zval): 24 bytes.
      Variable value (zvalue_value): 16 bytes.

Usage in production

PHP Meminfo can be used in production, as it does not have any impact on performances outside of the call to the meminfo functions.

Nevertheless, production environment is not where you debug ;)

Other memory debugging tools for PHP

• XDebug (http://www.xdebug.net) With the trace feature and the memory delta option (tool see XDebug documentation), you can trace function memory usage. You can use the provided script to get an aggregated view (TODO link)

• PHP Memprof (https://github.com/arnaud-lb/php-memory-profiler) Provides aggregated data about memory usage by functions. Far less resource intensive than a full trace from XDebug.

Troubleshooting

"Call to undefined function" when calling meminfo_* functions

It certainly means the extension is not enabled.

Check the PHP Info output and look for the MemInfo data.

To see the PHP Info output, just create a page calling the phpinfo(); function, and load it from your browser, or call php -i from command line.

Credits

Thanks to Derick Rethans on his inspirational work on the essential XDebug. See http://www.xdebug.org/