fbc0fe9a2e
In set_append_rel_size(), we currently set rel->tuples to rel->rows for an appendrel. Generally, rel->tuples is the raw number of tuples in the relation and rel->rows is the estimated number of tuples after the relation's restriction clauses have been applied. Although an appendrel itself doesn't directly enforce any quals today, its child relations may. Therefore, setting rel->tuples equal to rel->rows for an appendrel isn't always appropriate. Doing so can lead to issues in cost estimates in some cases. For instance, when estimating the number of distinct values from an appendrel, we would not be able to adjust the estimate based on the restriction selectivity. This patch addresses this by setting an appendrel's tuples to the total number of tuples accumulated from each live child, which better aligns with reality. This is arguably a bug, but nobody has complained about that until now, so no back-patch. Author: Richard Guo <guofenglinux@gmail.com> Reviewed-by: Tender Wang <tndrwang@gmail.com> Reviewed-by: Alena Rybakina <a.rybakina@postgrespro.ru> Discussion: https://postgr.es/m/CAMbWs4_TG_+kVn6fjG-5GYzzukrNK57=g9eUo4gsrUG26OFawg@mail.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/.