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During pruning and freezing in phase I of vacuum, we delay clearing all_visible and all_frozen in the presence of dead items. This allows opportunistic freezing if the page would otherwise be fully frozen, since those dead items are later removed in vacuum phase III. To move the VM update into the same WAL record that prunes and freezes tuples, we must know whether the page will be marked all-visible/all-frozen before emitting WAL. Previously we waited until after emitting WAL to update all_visible/all_frozen to their correct values. The only barrier to updating these flags immediately after deciding whether to opportunistically freeze was that while emitting WAL for a record freezing tuples, we use the pre-corrected value of all_frozen to compute the snapshot conflict horizon. By determining the conflict horizon earlier, we can update the flags immediately after making the opportunistic freeze decision. This is required to set the VM in the XLOG_HEAP2_PRUNE_VACUUM_SCAN record emitted by pruning and freezing. Author: Melanie Plageman <melanieplageman@gmail.com> Reviewed-by: Kirill Reshke <reshkekirill@gmail.com> Discussion: https://postgr.es/m/flat/CAAKRu_ZMw6Npd_qm2KM%2BFwQ3cMOMx1Dh3VMhp8-V7SOLxdK9-g%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.
Copyright and license information can be found in the file COPYRIGHT.
General documentation about this version of PostgreSQL can be found at https://www.postgresql.org/docs/devel/. In particular, information about building PostgreSQL from the source code can be found at https://www.postgresql.org/docs/devel/installation.html.
The latest version of this software, and related software, may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.