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: 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

PHP 5.5, 5.6, 7.0, 7.1, and 7.2.

May compiles and works with PHP 5.3 and 5.4 but hasn't been tested with these versions.

Installation

On macOS you can install or upgrade the extension using Homebrew

For exmaple, if you want to install PHP Meminfo for PHP 7.1, run:

$ brew install php71-meminfo

Compilation instructions

Compilation

From the root of the extension/php5 for PHP 5 or extension/php7 for PHP 7 directory:

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

Enabling the extension

Add the following line to your php.ini:

extension=meminfo.so

Installing analyzers

Analyzers allow to analyze a memory dump (see below).

$ cd analyzer
$ composer install

Usage

Dumping memory content

meminfo_dump(fopen('/tmp/my_dump_file.json', 'w'));

This function generates a dump of the PHP memory in a JSON format. This dump can be later analyzed by the provided analyzers.

This functions takes a stream handle as a parameter. It allows you to specify a file (ex fopen('/tmp/file.txt', 'w'), as well as to use standard output with the php://stdout stream.

Displaying a summary of items in memory

$ bin/analyzer summary <dump-file>

Arguments:
  dump-file             PHP Meminfo Dump File in JSON format

Example

$ bin/analyzer summary /tmp/my_dump_file.json
+----------+-----------------+-----------------------------+
| Type     | Instances Count | Cumulated Self Size (bytes) |
+----------+-----------------+-----------------------------+
| string   | 132             | 7079                        |
| MyClassA | 100             | 7200                        |
| array    | 10              | 720                         |
| integer  | 5               | 80                          |
| float    | 2               | 32                          |
| null     | 1               | 16                          |
+----------+-----------------+-----------------------------+

Querying the memory dump to find specific objects

$ bin/analyzer query [options] [--] <dump-file>

Arguments:
  dump-file              PHP Meminfo Dump File in JSON format

Options:
  -f, --filters=FILTERS  Filter on an attribute. Operators: =, ~. Example: class~User (multiple values allowed)
  -l, --limit=LIMIT      Number of results limit (default 10).
  -v                     Increase the verbosity

Example

$ bin/analyzer query -v -f "class=MyClassA" -f "is_root=0" /tmp/php_mem_dump.json
+----------------+-------------------+------------------------------+
| Item ids       | Item data         | Children                     |
+----------------+-------------------+------------------------------+
| 0x7f94a1877008 | Type: object      | myObjectName: 0x7f94a185cca0 |
|                | Class: MyClassA   |                              |
|                | Object Handle: 1  |                              |
|                | Size: 72 B        |                              |
|                | Is root: No       |                              |
+----------------+-------------------+------------------------------+
| 0x7f94a1877028 | Type: object      | myObjectName: 0x7f94a185cde0 |
|                | Class: MyClassA   |                              |
|                | Object Handle: 2  |                              |
|                | Size: 72 B        |                              |
|                | Is root: No       |                              |
+----------------+-------------------+------------------------------+
| 0x7f94a1877048 | Type: object      | myObjectName: 0x7f94a185cf20 |
|                | Class: MyClassA   |                              |
...

Displaying the reference path

The reference path is the path between a specific item in memory (identified by it's pointer address) and all the intermediary items up to the one item that is attached to a variable still alive in the program.

This path shows who are the items responsible for the memory leak of the specific item provided.

$ bin/analyzer ref-path <item-id> <dump-file>

Arguments:
  item-id               Item Id in 0xaaaaaaaa format
  dump-file             PHP Meminfo Dump File in JSON format

Options:
  -v                     Increase the verbosity

Example

$ bin/analyzer ref-path -v 0x7f94a1877068 /tmp/php_mem_dump.json
Found 1 paths
Path from 0x7f94a1856260
+--------------------+
| Id: 0x7f94a1877068 |
| Type: object       |
| Class: MyClassA    |
| Object Handle: 4   |
| Size: 72 B         |
| Is root: No        |
| Children count: 1  |
+--------------------+
         ^
         |
         3
         |
         |
+---------------------+
| Id: 0x7f94a185cb60  |
| Type: array         |
| Size: 72 B          |
| Is root: No         |
| Children count: 100 |
+---------------------+
         ^
         |
    second level
         |
         |
+--------------------+
| Id: 0x7f94a185ca20 |
| Type: array        |
| Size: 72 B         |
| Is root: No        |
| Children count: 1  |
+--------------------+
         ^
         |
    first level
         |
         |
+---------------------------+
| Id: 0x7f94a1856260        |
| Type: array               |
| Size: 72 B                |
| Is root: Yes              |
| Execution Frame: <GLOBAL> |
| Symbol Name: myRootArray  |
| Children count: 1         |
+---------------------------+

A worflow to find and understand memory leak by using PHP Meminfo

Hunting down memory leaks

Other memory debugging tools for PHP

• XDebug (https://xdebug.org/) 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_dump

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 the command line.

Why most tests are "skipped"?

While doing a make test, some test will need JSON capabilities. But The compilation system generates a clean env by removing all configuration directives that load extension. So if JSON capabilites are packaged as a separate extension (instead of being compiled directly in the PHP runtime), the tests will be skipped.

You may run them with the run-tests.php generated after the make test command, by providing the php executable:

$ TEST_PHP_EXECUTABLE=/usr/bin/php php run-tests.php

In this case, your tests will run with your local PHP configuration, including the loading of the JSON extension.

Credits

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