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In a USE_UNNAMED_SEMAPHORES build, the default on Linux and FreeBSD since commit ecb0d20a, we have an array of sem_t objects. This turned out to reduce performance compared to the previous default USE_SYSV_SEMAPHORES on an 8 socket system. Testing showed that the lost performance could be regained by padding the array elements so that they have their own cache lines. This matches what we do for similar hot arrays (see LWLockPadded, WALInsertLockPadded). Back-patch to 10, where unnamed semaphores were adopted as the default semaphore interface on those operating systems. Author: Thomas Munro Reviewed-by: Andres Freund Reported-by: Mithun Cy Tested-by: Mithun Cy, Tom Lane, Thomas Munro Discussion: https://postgr.es/m/CAD__OugYDM3O%2BdyZnnZSbJprSfsGFJcQ1R%3De59T3hcLmDug4_w%40mail.gmail.com
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/.