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When descending the tree for an insert, and there are multiple equally good pages we could insert to, make the choice in random. Previously, we would always choose the tuple with lowest offset number. That meant that when two non-leaf pages overlap - in the extreme case they might have exactly the same key - all but the first such page went unused. That wasn't optimal for space usage; if you deleted some tuples from the non-first pages, the space would never be reused. With this patch, the other pages are sometimes chosen too, although there's still a heavy bias towards low-offset tuples, so that we don't lose cache locality when doing a lot of inserts with similar keys. Original idea by Alexander Korotkov, although this patch version was written by me and copy-edited by Tom Lane.
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: http://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. Changes between all PostgreSQL releases are recorded in the file HISTORY. 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 http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.