Sixteen Locks Ought to Be Enough for Anybody

Automated excerpt

When PostgreSQL plans a query, it takes AccessShareLock on every relation the query might use. So a table with a primary key and 20 secondary indexes costs 22 relation locks per query: the table, the primary key index, and the 20 others the planner examined and discarded. If a query needs more than 16 relation locks, the overflow goes through the shared lock table, LWLocks and all.

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