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The old LWLock implementation had the problem that concurrent lock acquisitions required exclusively acquiring a spinlock. Often that could lead to acquirers waiting behind the spinlock, even if the actual LWLock was free. The new implementation doesn't acquire the spinlock when acquiring the lock itself. Instead the new atomic operations are used to atomically manipulate the state. Only the waitqueue, used solely in the slow path, is still protected by the spinlock. Check lwlock.c's header for an explanation about the used algorithm. For some common workloads on larger machines this can yield significant performance improvements. Particularly in read mostly workloads. Reviewed-By: Amit Kapila and Robert Haas Author: Andres Freund Discussion: 20130926225545.GB26663@awork2.anarazel.de |
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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/.