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Consistently avoid trusting a sample of only one page at the point that VACUUM determines a new reltuples for the target table (though only when the table is larger than a single page). This is follow-up work to commit 74388a1a, which added a heuristic to prevent reltuples from becoming distorted by successive VACUUM operations that each scan only a single heap page (which was itself more or less a bugfix for an issue in commit 44fa8488, which simplified VACUUM's handling of scanned pages). The original bugfix commit did not account for certain remaining cases that where not affected by its "2% of total relpages" heuristic. This happened with relations that are small enough that just one of its pages exceeded the 2% threshold, yet still big enough for VACUUM to deem skipping most of its pages via the visibility map worthwhile. reltuples could still become distorted over time with such a table, at least in scenarios where the VACUUM command is run repeatedly and without the table itself ever changing. Author: Peter Geoghegan <pg@bowt.ie> Discussion: https://postgr.es/m/CAH2-Wzk7d4m3oEbEWkWQKd+gz-eD_peBvdXVk1a_KBygXadFeg@mail.gmail.com Backpatch: 15-, where the rules for scanned pages changed.
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/.