The behaviour of these functions is affected by settings in php.ini.
|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.|
Here's a short explanation of the configuration directives.
PCRE's backtracking limit.
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).