Runtime Configuration

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

PCRE Configuration Options
Name Default Changeable Changelog
pcre.backtrack_limit "100000" 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.

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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User Contributed Notes 2 notes

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php at richardneill dot org
3 years ago
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.
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chris at ocproducts dot com
3 years ago
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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