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Previously aggregate transition values for hash and other forms of aggregation (i.e. sort and no group by) were represented differently. Hash based aggregation used a grouping set indexed array pointing to an array of transition values, whereas other forms of aggregation used one flattened array with the index being computed out of grouping set and transition offsets. That made upcoming changes hard, so represent both as grouping set indexed array of per-group data. As a nice side-effect this also makes aggregation slightly faster, because computing offsets with `transno + (setno * numTrans)` turns out not to be that cheap (too big for x86 lea for example). Author: Andres Freund Discussion: https://postgr.es/m/20171128003121.nmxbm2ounxzb6n2t@alap3.anarazel.de
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/.