5b9a058384
granted the lock when awakened; the signal now only means that the lock is potentially available. The waiting process must retry its attempt to get the lock when it gets to run. This allows the lock releasing process to re-acquire the lock later in its timeslice. Since LWLocks are usually held for short periods, it is possible for a process to acquire and release the same lock many times in a timeslice. The old spinlock-based implementation of these locks allowed for that; but the original coding of LWLock would force a process swap for each acquisition if there was any contention. Although this approach reopens the door to process starvation (a waiter might repeatedly fail to get the lock), the odds of that being a big problem seem low, and the performance cost of the previous approach is considerable.
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 several language bindings, including C, C++, Perl, Python, and Tcl, as well as drivers for JDBC and ODBC. 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 ftp://ftp.postgresql.org/pub/. For more information look at our web site located at http://www.postgresql.org/.