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5843659d09
Buildfarm members ayu and tern have sometimes shown a different plan than expected for this query. I'd been unable to reproduce that before today, but I finally realized what is happening. If there is a concurrent open transaction (probably an autovacuum run in the buildfarm, but this can also be arranged manually), then the index entries for the rows removed by the DELETE a few lines up are not killed promptly, causing a change in the planner's estimate of the extremal value of ft2.c1, which moves the rowcount estimate for "c1 > 1100" by enough to change the join plan from nestloop to hash. To fix, change the query condition to "c1 > 1000", causing the hash plan to be preferred whether or not a concurrent open transaction exists. Since this UPDATE is tailored to be a no-op, nothing else changes. Report: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=ayu&dt=2021-06-09%2022%3A45%3A48 Report: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=ayu&dt=2021-06-13%2022%3A38%3A18 Report: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=tern&dt=2021-06-20%2004%3A55%3A36
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/.