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When building a MergeAppendPath which has child paths that are not sorted correctly for the MergeAppend's sort order, we apply the cost of sorting those paths to the MergeAppendPath costs. Here we fix a bug where the number of tuples specified that needed to be sorted was effectively pg_class.reltuples rather than the number of expected row in the subpath. This effectively penalizes MergeAppend plans any time any filter is present on the MergeAppend subpath as the sort cost added is to sort all tuples in the table rather than just the ones expected the path to return. This did not affect UNION ALL type queries as the RelOptInfo tuples is set from the subquery's path rows. It does affect MergeAppends uses for inheritance and partitioned tables. This is a long-standing bug introduced when MergeAppend was first added in 11cad29c9. No backpatch as this could result in plan changes. Author: Alexander Kuzmenkov Reviewed-by: Ashutosh Bapat, Aleksander Alekseev, David Rowley Discussion: https://postgr.es/m/CALzhyqyhoXQDR-Usd_0HeWk%3DuqNLzoVeT8KhRoo%3DpV_KzgO3QQ%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/.