e369f37086
Since the WAL flush position only moves forward, it's safe to cache its previous value within each walsender process, and update from shared memory only once we've caught up to the previously-seen value. When there are many active walsenders, this makes for a very significant reduction in the amount of contention on the XLogCtl->info_lck spinlock. This patch also adjusts the logic so that we update our idea of the flush position after processing a WAL record, rather than beforehand. This may cause us to realize we're not caught up when the preceding coding would've thought that we were, but that seems all to the good; it may avoid a useless sleep-and-wakeup cycle. Back-patch to v12. The contention problem exists in prior branches, but it's much less severe (due to inefficiencies elsewhere) so there seems no need to take any risk of back-patching further. Pierre Ducroquet, reviewed by Julien Rouhaud Discussion: https://postgr.es/m/2931018.Vxl9zapr77@pierred-pdoc
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/.