4effd0844d
Commit b5a9b18c introduced block streaming infrastructure with a special fast path for all-cached scans, and commit b7b0f3f2 connected the infrastructure up to sequential scans. One of the fast path micro-optimizations had an unintended consequence: it interfered with parallel sequential scan's block range allocator (from commit 56788d21), which has its own ramp-up and ramp-down algorithm when handing out groups of pages to workers. A scan of an all-cached table could give extra blocks to one worker, when others had finished. In some plans (probably already very bad plans, such as the one reported by Alexander), the unfairness could be magnified. An internal buffer of 16 block numbers is removed, keeping just a single block buffer for technical reasons. Back-patch to 17. Reported-by: Alexander Lakhin <exclusion@gmail.com> Discussion: https://postgr.es/m/63a63690-dd92-c809-0b47-af05459e95d1%40gmail.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/.