The value n is the lock threshold. This is the number of inserts, updates, or deletes for a single table within a single transaction that will trigger a table-level lock when reached. For example, if the lock threshold is 1000 and a process starts a transaction and then inserts 2000 rows, after the 1001st row is inserted the process will attempt to acquire a table-level lock instead of continue to lock individual rows. This is to help keep the lock table from becoming too full.
Any integer. The default is 1000.
On the page System Administration > Configuration > SQL and Object Settings > General SQL Settings, in the Lock Threshold field, enter a number.