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If vacuum fails to remove a tuple with xmax older than VacuumCutoffs->OldestXmin and younger than GlobalVisState->maybe_needed, it will loop infinitely in lazy_scan_prune(), which compares tuples' visibility information to OldestXmin. Starting in version 14, which uses GlobalVisState for visibility testing during pruning, it is possible for GlobalVisState->maybe_needed to precede OldestXmin if maybe_needed is forced to go backward while vacuum is running. This can happen if a disconnected standby with a running transaction older than VacuumCutoffs->OldestXmin reconnects to the primary after vacuum initially calculates GlobalVisState and OldestXmin. Fix this by having vacuum always remove tuples older than OldestXmin during pruning. This is okay because the standby won't replay the tuple removal until the tuple is removable. Thus, the worst that can happen is a recovery conflict. Fixes BUG# 17257 Back-patched in versions 14-17 Author: Melanie Plageman Reviewed-by: Noah Misch, Peter Geoghegan, Robert Haas, Andres Freund, and Heikki Linnakangas Discussion: https://postgr.es/m/CAAKRu_Y_NJzF4-8gzTTeaOuUL3CcGoXPjXcAHbTTygT8AyVqag%40mail.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/.