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Testing done in 2011 by Tom Lane concluded that this is a win on Intel Xeons and AMD Opterons, but it was not changed back then, because of an old comment in tas() that suggested that it's a huge loss on older Opterons. However, didn't have separate TAS() and TAS_SPIN() macros back then, so the comment referred to doing a non-locked initial test even on the first access, in uncontended case. I don't have access to older Opterons, but I'm pretty sure that doing an initial unlocked test is unlikely to be a loss while spinning, even though it might be for the first access. We probably should do the same on 32-bit x86, but I'm afraid of changing it without any testing. Hence just add a note to the x86 implementation suggesting that we probably should do the same there. |
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| README.git | ||
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. Changes between all PostgreSQL releases are recorded in the file HISTORY. 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/.