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When min_parallel_relation_size was added, the only supported type of parallel scan was a parallel sequential scan, but there are pending patches for parallel index scan, parallel index-only scan, and parallel bitmap heap scan. Those patches introduce two new types of complications: first, what's relevant is not really the total size of the relation but the portion of it that we will scan; and second, index pages and heap pages shouldn't necessarily be treated in exactly the same way. Typically, the number of index pages will be quite small, but that doesn't necessarily mean that a parallel index scan can't pay off. Therefore, we introduce min_parallel_table_scan_size, which works out a degree of parallelism for scans based on the number of table pages that will be scanned (and which is therefore equivalent to min_parallel_relation_size for parallel sequential scans) and also min_parallel_index_scan_size which can be used to work out a degree of parallelism based on the number of index pages that will be scanned. Amit Kapila and Robert Haas Discussion: http://postgr.es/m/CAA4eK1KowGSYYVpd2qPpaPPA5R90r++QwDFbrRECTE9H_HvpOg@mail.gmail.com Discussion: http://postgr.es/m/CAA4eK1+TnM4pXQbvn7OXqam+k_HZqb0ROZUMxOiL6DWJYCyYow@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: 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. 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/.