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Eager freezing strategy avoids large build-ups of all-visible pages. It makes VACUUM trigger page-level freezing whenever doing so will enable the page to become all-frozen in the visibility map. This is useful for tables that experience continual growth, particularly strict append-only tables such as pgbench's history table. Eager freezing significantly improves performance stability by spreading out the cost of freezing over time, rather than doing most freezing during aggressive VACUUMs. It complements the insert autovacuum mechanism added by commit b07642db. VACUUM determines its freezing strategy based on the value of the new vacuum_freeze_strategy_threshold GUC (or reloption) with logged tables. Tables that exceed the size threshold use the eager freezing strategy. Unlogged tables and temp tables always use eager freezing strategy, since the added cost is negligible there. Non-permanent relations won't incur any extra overhead in WAL written (for the obvious reason), nor in pages dirtied (since any extra freezing will only take place on pages whose PD_ALL_VISIBLE bit needed to be set either way). VACUUM uses lazy freezing strategy for logged tables that fall under the GUC size threshold. Page-level freezing triggers based on the criteria established in commit 1de58df4, which added basic page-level freezing. Eager freezing is strictly more aggressive than lazy freezing. Settings like vacuum_freeze_min_age still get applied in just the same way in every VACUUM, independent of the strategy in use. The only mechanical difference between eager and lazy freezing strategies is that only the former applies its own additional criteria to trigger freezing pages. Note that even lazy freezing strategy will trigger freezing whenever a page happens to have required that an FPI be written during pruning, provided that the page will thereby become all-frozen in the visibility map afterwards (due to the FPI optimization from commit 1de58df4). The vacuum_freeze_strategy_threshold default setting is 4GB. This is a relatively low setting that prioritizes performance stability. It will be reviewed at the end of the Postgres 16 beta period. Author: Peter Geoghegan <pg@bowt.ie> Reviewed-By: Jeff Davis <pgsql@j-davis.com> Reviewed-By: Andres Freund <andres@anarazel.de> Reviewed-By: Matthias van de Meent <boekewurm+postgres@gmail.com> Discussion: https://postgr.es/m/CAH2-WzkFok_6EAHuK39GaW4FjEFQsY=3J0AAd6FXk93u-Xq3Fg@mail.gmail.com
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: https://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. 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 https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.