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Several upcoming performance/scalability improvements require atomic operations. This new API avoids the need to splatter compiler and architecture dependent code over all the locations employing atomic ops. For several of the potential usages it'd be problematic to maintain both, a atomics using implementation and one using spinlocks or similar. In all likelihood one of the implementations would not get tested regularly under concurrency. To avoid that scenario the new API provides a automatic fallback of atomic operations to spinlocks. All properties of atomic operations are maintained. This fallback - obviously - isn't as fast as just using atomic ops, but it's not bad either. For one of the future users the atomics ontop spinlocks implementation was actually slightly faster than the old purely spinlock using implementation. That's important because it reduces the fear of regressing older platforms when improving the scalability for new ones. The API, loosely modeled after the C11 atomics support, currently provides 'atomic flags' and 32 bit unsigned integers. If the platform efficiently supports atomic 64 bit unsigned integers those are also provided. To implement atomics support for a platform/architecture/compiler for a type of atomics 32bit compare and exchange needs to be implemented. If available and more efficient native support for flags, 32 bit atomic addition, and corresponding 64 bit operations may also be provided. Additional useful atomic operations are implemented generically ontop of these. The implementation for various versions of gcc, msvc and sun studio have been tested. Additional existing stub implementations for * Intel icc * HUPX acc * IBM xlc are included but have never been tested. These will likely require fixes based on buildfarm and user feedback. As atomic operations also require barriers for some operations the existing barrier support has been moved into the atomics code. Author: Andres Freund with contributions from Oskari Saarenmaa Reviewed-By: Amit Kapila, Robert Haas, Heikki Linnakangas and Álvaro Herrera Discussion: CA+TgmoYBW+ux5-8Ja=Mcyuy8=VXAnVRHp3Kess6Pn3DMXAPAEA@mail.gmail.com, 20131015123303.GH5300@awork2.anarazel.de, 20131028205522.GI20248@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/.