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The more efficient hashtable speeds up hash-aggregations with more than a few hundred groups significantly. Improvements of over 120% have been measured. Due to the the different hash table queries that not fully determined (e.g. GROUP BY without ORDER BY) may change their result order. The conversion is largely straight-forward, except that, due to the static element types of simplehash.h type hashes, the additional data some users store in elements (e.g. the per-group working data for hash aggregaters) is now stored in TupleHashEntryData->additional. The meaning of BuildTupleHashTable's entrysize (renamed to additionalsize) has been changed to only be about the additionally stored size. That size is only used for the initial sizing of the hash-table. Reviewed-By: Tomas Vondra Discussion: <20160727004333.r3e2k2y6fvk2ntup@alap3.anarazel.de> |
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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/.