Manual:InitEditCount.php/en

Details
initEditCount.php file is a maintenance script to init the   database field based on the number of rows in the revision table.

Options
Background mode will be automatically used if multiple servers are listed in the load balancer, usually indicating a replication environment. So first it calculates counts of replica DB if it found it then script run job in background mode to avoids locking tables or lagging replica DBs with large updates.