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Teach nbtree forward index scans to check the high key before moving to the right sibling page in the hope of finding that it isn't actually necessary to do so. The new check may indicate that the scan definitely cannot find matching tuples to the right, ending the scan immediately. We already opportunistically force a similar "continuescan orientated" key check of the final non-pivot tuple when it's clear that it cannot be returned to the scan due to being dead-to-all. The new high key check is complementary. The new approach for forward scans is more effective than checking the final non-pivot tuple, especially with composite indexes and non-unique indexes. The improvements to the logic for picking a split point added by commit fab25024 make it likely that relatively dissimilar high keys will appear on a page. A distinguishing key value that can only appear on non-pivot tuples on the right sibling page will often be present in leaf page high keys. Since forcing the final item to be key checked no longer makes any difference in the case of forward scans, the existing extra key check is now only used for backwards scans. Backward scans continue to opportunistically check the final non-pivot tuple, which is actually the first non-pivot tuple on the page (not the last). Note that even pg_upgrade'd v3 indexes make use of this optimization. Author: Peter Geoghegan, Heikki Linnakangas Reviewed-By: Heikki Linnakangas Discussion: https://postgr.es/m/CAH2-WzkOmUduME31QnuTFpimejuQoiZ-HOf0pOWeFZNhTMctvA@mail.gmail.com
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/.