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Igbinary is a drop in replacement for the standard php serializer. Instead of the time and space consuming textual representation used by PHP's serialize, igbinary stores php data structures in a compact binary form. Memory savings are significant when using memcached, APCu, or similar memory based storages for serialized data. The typical reduction in storage requirements are around 50%. The exact percentage depends on your data.

Unserialization performance is at least on par with the standard PHP serializer, and is much faster for repetitive data. Serialization performance depends on the igbinary.compact_strings option which enables duplicate string tracking. String are inserted to a hash table, which adds some overhead when serializing. In usual scenarios this does not have much of an impact, because the typical usage pattern is "serialize rarely, unserialize often". With the compact_strings option enabled, igbinary is usually a bit slower than the standard serializer. Without it, igbinary is a bit faster.


  • Support for the same data types as the standard PHP serializer: null, bool, int, float, string, array and object.
  • __autoload & unserialize_callback_func
  • __sleep & __wakeup
  • __serialize & __unserialize (only used in php 7.4+)
  • Serializable -interface
  • Data portability between platforms (32/64bit, endianness)
  • Tested on Linux amd64, Linux ARM, Mac OSX x86, HP-UX PA-RISC and NetBSD sparc64
  • Hooks up to the APCu in-memory key-value store as a serialization handler.
  • Compatible with 7.0 – 8.0 (The older igbinary 2.x releases support 5.2 – 5.6, 7.0 – 7.3)

Implementation details

Storing complex PHP data structures such as arrays of associative arrays with the standard PHP serializer is not very space efficient. The main reasons of this inefficiency are listed below, in order of significance (at least in our applications):

  1. Array keys, property names, and class names are repeated redundantly.
  2. Numerical values are plain text.
  3. Human readability adds some overhead.

Igbinary uses two strategies to minimize the size of the serialized output.

  1. Repeated strings are stored only once (this also includes class and property names). Collections of objects benefit significantly from this. See the igbinary.compact_strings option.

  2. Integer values are stored in the smallest primitive data type available: 123 = int8_t, 1234 = int16_t, 123456 = int32_t ... and so on.

  3. ( Well, it is not human readable ;)

How to use

Add the following lines to your php.ini:

; Load igbinary extension

; Use igbinary as session serializer

; Enable or disable compacting of duplicate strings
; The default is On.

; If uncommented, use igbinary as the serializer of APCu
; (APCu 5.1.10 or newer is strongly recommended)

Then, in your php code, replace serialize and unserialize function calls with igbinary_serialize and igbinary_unserialize.



If PHP was installed through your package manager, the package manager may also contain prebuilt packages for igbinary (with a package name similar to php-igbinary).

  • The packages from some package managers and OS versions may be out of date and have known bugs. The latest release of igbinary is The Latest Stable Version

Igbinary may also be installed with the command pecl install igbinary (You will need to enable igbinary in php.ini)

Alternately, you may wish to build from source


pecl install igbinary is the recommended installation method (You will need to enable igbinary in php.ini)

Alternately, you may wish to build from source.

Installing on Windows

Prebuilt DLLs can be downloaded from PECL.

If you are a contributor to/packager of igbinary, or need to build from source, see

Building from source

  1. phpize

  2. ./configure

    • With GCC: ./configure CFLAGS="-O2 -g" --enable-igbinary
    • With ICC (Intel C Compiler) ./configure CFLAGS=" -no-prec-div -O3 -xO -unroll2 -g" CC=icc --enable-igbinary
    • With clang: ./configure CC=clang CFLAGS="-O0 -g" --enable-igbinary
  3. make

  4. make test

  5. make install

  6. is installed to the default extension directory

Bugs & Contributions

Mailing list for bug reports and other development discussion can be found at (no longer used)

File bug reports at

The preferred way to contribute is with pull requests. Feel free to fork this at

See for advice for testing patches.

See for information about how igbinary is implemented

Utilizing in other extensions

Igbinary can be called from other extensions fairly easily. Igbinary installs its header file to ext/igbinary/igbinary.h. There are just two straightforward functions: igbinary_serialize and igbinary_unserialize. Look at igbinary.h for prototypes and usage.

Add PHP_ADD_EXTENSION_DEP(yourextension, igbinary) to your config.m4 in case someone wants to compile both of them statically into php.


Where does the name "igbinary" come from? There was once a similar project called fbinary but it has disappeared from the Internet a long time ago. Its architecture wasn't particularly clean either. IG is an abbreviation for a Finnish social networking site IRC-Galleria (


Igbinary is a drop in replacement for the standard php serializer.







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