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Previously we did a ExecProject() for each individual aggregate argument. That turned out to be a performance bottleneck in queries with multiple aggregates. Doing all the argument computations in one ExecProject() is quite a bit cheaper because ExecProject's fastpath can do the work at once in a relatively tight loop, and because it can get all the required columns with a single slot_getsomeattr and save some other redundant setup costs. Author: Andres Freund Reviewed-By: Heikki Linnakangas Discussion: https://postgr.es/m/20161103110721.h5i5t5saxfk5eeik@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: http://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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.