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It was previously thought that remove_useless_groupby_columns() needed to keep track of which constraints the generated plan depended upon, however, this is unnecessary. The confusion likely arose regarding this because of check_functional_grouping(), which does need to track the dependency to ensure VIEWs with columns which are functionally dependant on the GROUP BY remain so. For remove_useless_groupby_columns(), cached plans will just become invalidated when the primary key's underlying index is removed through the normal relcache invalidation code. Here we just remove the unneeded code which records the dependency and updates the comments. The previous comments claimed that we could not use UNIQUE constraints for the same optimization due to lack of a pg_constraint record for NOT NULL constraints (which are required because NULLs can be duplicated in a unique index). Since we don't actually need a pg_constraint record to handle the invalidation, it looks like we could add code to do this in the future. But not today. We're not really fixing any bug in the code here, this fix is just to set the record straight on UNIQUE constraints. This code was added back in 9.6, but due to lack of any bug, we'll not be backpatching this. Reviewed-by: Tom Lane Discussion: https://postgr.es/m/CAApHDvrdYa=VhOoMe4ZZjZ-G4ALnD-xuAeUNCRTL+PYMVN8OnQ@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. 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/.