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perform_pullup_replace_vars() knows how to scan the whole parent query tree when we are replacing Vars during a subquery flattening operation. However, for the specific case of flattening a UNION ALL leaf query, that's mostly wasted work: the only place where relevant Vars could exist is in the AppendRelInfo that we just made for this leaf. Teaching perform_pullup_replace_vars() to just deal with that and exit is worthwhile because, if we have N such subqueries to pull up, we were spending O(N^2) work uselessly mutating the AppendRelInfos for all the other subqueries. While we're at it, avoid calling substitute_phv_relids if there are no PlaceHolderVars, and remove an obsolete check of parse->hasSubLinks. Andrey Lepikhov and Tom Lane Discussion: https://postgr.es/m/703c09a2-08f3-d2ec-b33d-dbecd62428b8@postgrespro.ru
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/.