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This has the advantage that the comparator expression, the table's slot, etc do not have to be rebuilt. Additionally the simplehash.h hashtable within the tuple hashtable now keeps its previous size and doesn't need to be reallocated. That both reduces allocator overhead, and improves performance in cases where the input estimation was off by a significant factor. To avoid an API/ABI break, the new parameter is exposed via the new BuildTupleHashTableExt(), and BuildTupleHashTable() now is a wrapper around the former, that continues to allocate the table itself in the tablecxt. Using this fixes performance issues discovered in the two bugs referenced. This commit however has not converted the callers, that's done in a separate commit. Bug: #15592 #15486 Reported-By: Jakub Janeček, Dmitry Marakasov Author: Andres Freund Discussion: https://postgr.es/m/15486-05850f065da42931@postgresql.org https://postgr.es/m/20190114180423.ywhdg2iagzvh43we@alap3.anarazel.de Backpatch: 11, this is a prerequisite for other fixes
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/.