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Prior to this, Bitmapsets could contain trailing words which had no members set. Many places in bitmapset.c had to loop over trailing words to check for empty words. If we ensure we always remove these trailing zero words then we can perform various optimizations such as fast pathing bms_is_subset to return false when 'a' has more words than 'b'. A similar optimization is possible in bms_equal. Both of these together can yield quite significant performance increases in the query planner when querying a partitioned table with around 100 or more partitions. While we're at it, since the minimum number of words a Bitmapset can contain is 1, we can make use of do/while loops instead of for loops when looping over all words in a set. This means checking the loop condition 1 less time, which for single-word sets cuts the loop condition checks in half. Author: David Rowley Reviewed-by: Yuya Watari Discussion: https://postgr.es/m/CAApHDvr5O41MuUjw0DQKqmAnv7QqvmLqXReEd5o4nXTzWp8-+w@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/.