PHP: Runtime Configuration

[edit] Last updated: Fri, 10 Feb 2012

Runtime Configuration

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

**PCRE Configuration Options**
Name	Default	Changeable	Changelog
pcre.backtrack_limit	"1000000"	PHP_INI_ALL	Available since PHP 5.2.0.
pcre.recursion_limit	"100000"	PHP_INI_ALL	Available since PHP 5.2.0.

For further details and definitions of the PHP_INI_* modes, see the Where a configuration setting may be set.

Here's a short explanation of the configuration directives.

pcre.backtrack_limit integer: PCRE's backtracking limit. Defaults to 100000 for PHP < 5.3.7.
pcre.recursion_limit integer: PCRE's recursion limit. Please note that if you set this value to a high number you may consume all the available process stack and eventually crash PHP (due to reaching the stack size limit imposed by the Operating System).

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php at richardneill dot org 14-Jan-2011 09:55


pcre.backtrack_limit defaults to 100k.  This is rather conservative.

It is limited by RAM size, not the ulimit on stack-size.



On a (2009-era) netbook, I can set pcre.backtrack_limit to 100 million, and the regex will happily process a 90 million character string in about 3 seconds. YMMV.

chris at ocproducts dot com 02-Jul-2010 07:42


pcre.backtrack_limit sets the maximum bind length PREG calls (e.g. preg_replace_callback) can make. However the actual maximum seems to be approximately half the value set here, possibly due to the character encoding that PCRE runs with internally.

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