Manual:$wgAllowSlowParserFunctions

Performance hacks and limits: $wgAllowSlowParserFunctions
Allow slow parser functions.
Introduced in version:1.7.0 (r15276)
Removed in version:Still in use
Allowed values:(boolean)
Default value:false

Details

Enables the magic word {{PAGESINNAMESPACE}}. After that, you can go to Special:Version to check for the existence of the proper parser hook.