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The planner doesn't make any use of root->total_table_pages until it estimates costs of indexscans, so we don't need to compute it as early as that's currently done. By doing the calculation between set_base_rel_sizes and set_base_rel_pathlists, we can omit relations that get removed from the query by partition pruning or constraint exclusion, which seems like a more accurate basis for costing. (Historical note: I think at the time this code was written, there was not a separation between the "set sizes" and "set pathlists" steps, so that this approach would have been impossible at the time. But now that we have that separation, this is clearly the better way to do things.) David Rowley, reviewed by Edmund Horner Discussion: https://postgr.es/m/CAKJS1f-NG1mRM0VOtkAG7=ZLQWihoqees9R4ki3CKBB0-fRfCA@mail.gmail.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/.