137805f89a
In cases where joins use multiple columns we currently assess each join separately causing gross mis-estimates for join cardinality. This patch adds use of FK information for the first time into the planner. When FKs are present and we have multi-column join information, plan estimates will be drastically improved. Cases with multiple FKs are handled, though partial matches are ignored currently. Net effect is substantial performance improvements for joins in many common cases. Additional planning time is isolated to cases that are currently performing poorly, measured at 0.08 - 0.15 ms. Please watch for planner performance regressions; circumstances seem unlikely but the law of unintended consequences may apply somewhen. Additional complex tests welcome to prove this before release. Tests can be performed using SET enable_fkey_estimates = on | off using scripts provided during Hackers discussions, message id: 552335D9.3090707@2ndquadrant.com Authors: Tomas Vondra and David Rowley Reviewed and tested by Simon Riggs, adding comments only |
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README
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/.