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If we don't have to return any columns from heap tuples, and there's no need to recheck qual conditions, and the heap page is all-visible, then we can skip fetching the heap page altogether. Skip prefetching pages too, when possible, on the assumption that the recheck flag will remain the same from one page to the next. While that assumption is hardly bulletproof, it seems like a good bet most of the time, and better than prefetching pages we don't need. This commit installs the executor infrastructure, but doesn't change any planner cost estimates, thus possibly causing bitmap scans to not be chosen in cases where this change renders them the best choice. I (tgl) am not entirely convinced that we need to account for this behavior in the planner, because I think typically the bitmap scan would get chosen anyway if it's the best bet. In any case the submitted patch took way too many shortcuts, resulting in too many clearly-bad choices, to be committable. Alexander Kuzmenkov, reviewed by Alexey Chernyshov, and whacked around rather heavily by me. Discussion: https://postgr.es/m/239a8955-c0fc-f506-026d-c837e86c827b@postgrespro.ru
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/.