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It is possible that the tail XID of pg_serial/ gets ahead of its head XID, which would cause the truncation of pg_serial/ done during checkpoints to show up as a "wraparound" LOG in SimpleLruTruncate(), which is confusing. This also wastes a bit of disk space until the head page is reclaimed again. CheckPointPredicate() is changed so as the cutoff page for the truncation is switched to the head page if the tail XID has advanced beyond the head XID, rather than the tail page. This prevents the confusing LOG message about a wraparound while allowing some truncation to be done to cut in disk space. This could be considered as a bug fix, but the original behavior is harmless as well, resulting only in disk space temporarily wasted, so no backpatch is done. Author: Sami Imseih Reviewed-by: Heikki Linnakangas, Michael Paquier Discussion: https://postgr.es/m/755E19CA-D02C-4A4C-80D3-74F775410C48@amazon.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/.