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This speeds up reassigning locks to the parent owner, when the transaction holds a lot of locks, but only a few of them belong to the current resource owner. This is particularly helps pg_dump when dumping a large number of objects. The cache can hold up to 15 locks in each resource owner. After that, the cache is marked as overflowed, and we fall back to the old method of scanning the whole local lock table. The tradeoff here is that the cache has to be scanned whenever a lock is released, so if the cache is too large, lock release becomes more expensive. 15 seems enough to cover pg_dump, and doesn't have much impact on lock release. Jeff Janes, reviewed by Amit Kapila and Heikki Linnakangas.
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Changes between all PostgreSQL releases are recorded in the file HISTORY. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.