3373c71553
Previously in order to determine which ECs a relation had members in, we had to loop over all ECs stored in PlannerInfo's eq_classes and check if ec_relids mentioned the relation. For the most part, this was fine, as generally, unless queries were fairly complex, the overhead of performing the lookup would have not been that significant. However, when queries contained large numbers of joins and ECs, the overhead to find the set of classes matching a given set of relations could become a significant portion of the overall planning effort. Here we allow a much more efficient method to access the ECs which match a given relation or set of relations. A new Bitmapset field in RelOptInfo now exists to store the indexes into PlannerInfo's eq_classes list which each relation is mentioned in. This allows very fast lookups to find all ECs belonging to a single relation. When we need to lookup ECs belonging to a given pair of relations, we can simply bitwise-AND the Bitmapsets from each relation and use the result to perform the lookup. We also take the opportunity to write a new implementation of generate_join_implied_equalities which makes use of the new indexes. generate_join_implied_equalities_for_ecs must remain as is as it can be given a custom list of ECs, which we can't easily determine the indexes of. This was originally intended to fix the performance penalty of looking up foreign keys matching a join condition which was introduced by 100340e2d. However, we're speeding up much more than just that here. Author: David Rowley, Tom Lane Reviewed-by: Tom Lane, Tomas Vondra Discussion: https://postgr.es/m/6970.1545327857@sss.pgh.pa.us
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: https://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 https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.