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Joel Jacobson reported that deep nesting of trivial (flattenable) views results in O(N^3) growth of planning time for N-deep nesting. It turns out that a large chunk of this cost comes from copying around the "subquery" sub-tree of each view's RTE_SUBQUERY RTE. But once we have successfully flattened the subquery, we don't need that anymore, because the planner isn't going to do anything else interesting with that RTE. We already zap the subquery pointer during setrefs.c (cf. add_rte_to_flat_rtable), but it's useless baggage earlier than that too. Clearing the pointer as soon as pull_up_simple_subquery is done with the RTE reduces the cost from O(N^3) to O(N^2); which is still not great, but it's quite a lot better. Further improvements will require rethinking of the RTE data structure, which is being considered in another thread. Patch by me; thanks to Dean Rasheed for review. Discussion: https://postgr.es/m/797aff54-b49b-4914-9ff9-aa42564a4d7d@www.fastmail.com |
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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: 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/.