Controls when the server acquires individual row locks for a table.
If the subsume_row_locks option is On (the default) then whenever a table t is locked exclusively with LOCK TABLE t IN EXCLUSIVE MODE, the server no longer acquires individual row locks for t.
This can result in a significant performance improvement if extensive updates are made to t in a single transaction, especially if t is large relative to cache size. It also allows for atomic update operations that are larger than the lock table can currently handle (approximately 2-4 million rows).
When this option is On, keyset cursors over a table locked in this fashion will return row changed warnings for every row in the cursor, if any row in the database has been modified. Note that the server could turn an updatable cursor with an ORDER BY into a keyset cursor as a result.