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Teach nbtree to give some consideration to how "distinguishing" candidate leaf page split points are. This should not noticeably affect the balance of free space within each half of the split, while still making suffix truncation truncate away significantly more attributes on average. The logic for choosing a leaf split point now uses a fallback mode in the case where the page is full of duplicates and it isn't possible to find even a minimally distinguishing split point. When the page is full of duplicates, the split should pack the left half very tightly, while leaving the right half mostly empty. Our assumption is that logical duplicates will almost always be inserted in ascending heap TID order with v4 indexes. This strategy leaves most of the free space on the half of the split that will likely be where future logical duplicates of the same value need to be placed. The number of cycles added is not very noticeable. This is important because deciding on a split point takes place while at least one exclusive buffer lock is held. We avoid using authoritative insertion scankey comparisons to save cycles, unlike suffix truncation proper. We use a faster binary comparison instead. Note that even pg_upgrade'd v3 indexes make use of these optimizations. Benchmarking has shown that even v3 indexes benefit, despite the fact that suffix truncation will only truncate non-key attributes in INCLUDE indexes. Grouping relatively similar tuples together is beneficial in and of itself, since it reduces the number of leaf pages that must be accessed by subsequent index scans. Author: Peter Geoghegan Reviewed-By: Heikki Linnakangas Discussion: https://postgr.es/m/CAH2-WzmmoLNQOj9mAD78iQHfWLJDszHEDrAzGTUMG3mVh5xWPw@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/.