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The select_outer_pathkeys_for_merge function made an attempt to build the merge join pathkeys in the same order as query_pathkeys. This was done as it may have led to no sort being required for an ORDER BY or GROUP BY clause in the upper planner. However, this restriction seems overly strict as it required that we match the query_pathkeys entirely or we don't bother putting the merge join pathkeys in that order. Here we relax this rule so that we use a prefix of the query_pathkeys providing that prefix matches all of the join quals. This may provide the upper planner with partially sorted input which will allow the use of incremental sorts instead of full sorts. Author: David Rowley Reviewed-by: Richard Guo Discussion: https://postgr.es/m/CAApHDvrtZu0PHVfDPFM4Yx3jNR2Wuwosv+T2zqa7LrhhBr2rRg@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/.