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The previous coding in plancache.c essentially used 10% of the estimated runtime as its cost estimate for planning. This can be pretty bogus, especially when the estimated runtime is very small, such as in a simple expression plan created by plpgsql, or a simple INSERT ... VALUES. While we don't have a really good handle on how planning time compares to runtime, it seems reasonable to use an estimate based on the number of relations referenced in the query, with a rather large multiplier. This patch uses 1000 * cpu_operator_cost * (nrelations + 1), so that even a trivial query will be charged 1000 * cpu_operator_cost for planning. This should address the problem reported by Marc Cousin and others that 9.2 and up prefer custom plans in cases where the planning time greatly exceeds what can be saved.
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. Changes between all PostgreSQL releases are recorded in the file HISTORY. 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/.