459e7bf8e2
The optimization does not take the removal of TIDs by a concurrent vacuum into account. The concurrent vacuum can remove dead TIDs and make pages ALL_VISIBLE while those dead TIDs are referenced in the bitmap. This can lead to a skip_fetch scan returning too many tuples. It likely would be possible to implement this optimization safely, but we don't have the necessary infrastructure in place. Nor is it clear that it's worth building that infrastructure, given how limited the skip_fetch optimization is. In the backbranches we just disable the optimization by always passing need_tuples=true to table_beginscan_bm(). We can't perform API/ABI changes in the backbranches and we want to make the change as minimal as possible. Author: Matthias van de Meent <boekewurm+postgres@gmail.com> Reported-By: Konstantin Knizhnik <knizhnik@garret.ru> Discussion: https://postgr.es/m/CAEze2Wg3gXXZTr6_rwC+s4-o2ZVFB5F985uUSgJTsECx6AmGcQ@mail.gmail.com Backpatch-through: 13
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/.