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497bac7d29
This code relied on pointer equality to identify which restriction clauses also appear in the indexquals (and, therefore, don't need to be applied as simple filter conditions). That was okay once upon a time, years ago, before we introduced the equivalence-class machinery. Now there's about a 50-50 chance that an equality clause appearing in the indexquals will be the mirror image (commutator) of its mate in the restriction list. When that happens, we'd erroneously think that the clause would be re-evaluated at each visited row, and therefore inflate the cost estimate for the indexscan by the clause's cost. Add some logic to catch this case. It seems to me that it continues not to be worthwhile to expend the extra predicate-proof work that createplan.c will do on the finally-selected plan, but this case is common enough and cheap enough to handle that we should do so. This will make a small difference (about one cpu_operator_cost per row) in simple cases; but in situations where there's an expensive function in the indexquals, it can make a very large difference, as seen in recent example from Jeff Janes. This is a long-standing bug, but I'm hesitant to back-patch because of the possibility of destabilizing plan choices that people may be happy with. |
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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/.