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We've had support for using unnamed POSIX semaphores instead of System V semaphores for quite some time, but it was not used by default on any platform. Since many systems have rather small limits on the number of SysV semaphores allowed, it seems desirable to switch to POSIX semaphores where they're available and don't create performance or kernel resource problems. Experimentation by me shows that unnamed POSIX semaphores are at least as good as SysV semaphores on Linux, and we previously had a report from Maksym Sobolyev that FreeBSD is significantly worse with SysV semaphores than POSIX ones. So adjust those two platforms to use unnamed POSIX semaphores, if configure can find the necessary library functions. If this goes well, we may switch other platforms as well, but it would be advisable to test them individually first. It's not currently contemplated that we'd encourage users to select a semaphore API for themselves, but anyone who wants to experiment can add PREFERRED_SEMAPHORES=UNNAMED_POSIX (or NAMED_POSIX, or SYSV) to their configure command line to do so. I also tweaked configure to report which API it's selected, mainly so that we can tell that from buildfarm reports. I did not touch the user documentation's discussion about semaphores; that will need some adjustment once the dust settles. Discussion: <8536.1475704230@sss.pgh.pa.us>
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/.