Manual:$wgDebugLogGroups/en

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.

If a group is configured in, then all debug messages with the according group key will be logged to that file, also if   is not set! With other words: If a group key is configured in, messages will be written, even if an empty value of   generally disables debugging.}}

Log destinations may be one of the following:


 * false to completely remove from the output, including from $wgDebugLogFile.
 * string values specifying a filename or URI.
 * associative array with keys:
 * 'destination' desired filename or URI.
 * 'sample' an integer value, specifying a sampling factor (optional)
 * 'level' A \Psr\Log\LogLevel constant, indicating the minimum level log (optional, since 1.25)

When  is set to a non-default value,   will probably be ignored, and the method of configuring log files will be determined by whatever logging system is invoked by.

Example
This example logs debug messages of group "ConfirmEditExtension" to "debug-ext_confirmedit.log" and those of group "SpamRegex" to "debug-spam.log".

Example:

Advanced example: