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DropRelFileNodeBuffers, DropDatabaseBuffers, FlushRelationBuffers, and FlushDatabaseBuffers have to scan the whole shared_buffers pool because we have no index structure that would find the target buffers any more efficiently than that. This gets expensive with large NBuffers. We can shave some cycles from these loops by prechecking to see if the current buffer is interesting before we acquire the buffer header lock. Ordinarily such a test would be unsafe, but in these cases it should be safe because we are already assuming that the caller holds a lock that prevents any new target pages from being loaded into the buffer pool concurrently. Therefore, no buffer tag should be changing to a value of interest, only away from a value of interest. So a false negative match is impossible, while a false positive is safe because we'll recheck after acquiring the buffer lock. Initial testing says that this speeds these loops by a factor of 2X to 3X on common Intel hardware. Patch for DropRelFileNodeBuffers by Jeff Janes (based on an idea of Heikki's); extended to the remaining sequential scans by Tom Lane |
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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. 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/.