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LockBufferForCleanup() acquires a cleanup lock unconditionally, and ConditionalLockBufferForCleanup() acquires a cleanup lock if it is possible to do so without waiting; this patch adds a new API, IsBufferCleanupOK(), which tests whether an exclusive lock already held happens to be a cleanup lock. This is possible because a cleanup lock simply means an exclusive lock plus the assurance any other pins on the buffer are newer than our own pin. Therefore, just as the existing functions decide that the exclusive lock that they've just taken is a cleanup lock if they observe the pin count to be 1, this new function allows us to observe that the pin count is 1 on a buffer we've already locked. This is useful in situations where a backend definitely wishes to modify the buffer and also wishes to perform cleanup operations if possible. The patch to eliminate heavyweight locking by hash indexes uses this, and it may have other applications as well. Amit Kapila, per a suggestion from me. Some comment adjustments by me as well.
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/.