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This patch replaces WALInsertLock with a number of WAL insertion slots, allowing multiple backends to insert WAL records to the WAL buffers concurrently. This is particularly useful for parallel loading large amounts of data on a system with many CPUs. This has one user-visible change: switching to a new WAL segment with pg_switch_xlog() now fills the remaining unused portion of the segment with zeros. This potentially adds some overhead, but it has been a very common practice by DBA's to clear the "tail" of the segment with an external pg_clearxlogtail utility anyway, to make the WAL files compress better. With this patch, it's no longer necessary to do that. This patch adds a new GUC, xloginsert_slots, to tune the number of WAL insertion slots. Performance testing suggests that the default, 8, works pretty well for all kinds of worklods, but I left the GUC in place to allow others with different hardware to test that easily. We might want to remove that before release. Reviewed by Andres Freund. |
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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. 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/.