Manual:$wgDebugLogGroups

Details
Set to an array of log group keys to filenames.

If set,   output for that group will go to that file instead of the regular  .

Useful for enabling selective logging in production.

Example
This example logs debug messages of group "ConfirmEditExtension" to "ext_confirmedit.log" and those of groups "FCKeditor" and "FCKeditorExtension" to "ext_fckeditor.log".