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Previously, we used an lwlock that was held from the time we began seeking a candidate buffer until the time when we found and pinned one, which is disastrous for concurrency. Instead, use a spinlock which is held just long enough to pop the freelist or advance the clock sweep hand, and then released. If we need to advance the clock sweep further, we reacquire the spinlock once per buffer. This represents a significant increase in atomic operations around buffer eviction, but it still wins on many workloads. On others, it may result in no gain, or even cause a regression, unless the number of buffer mapping locks is also increased. However, that seems like material for a separate commit. We may also need to consider other methods of mitigating contention on this spinlock, such as splitting it into multiple locks or jumping the clock sweep hand more than one buffer at a time, but those, too, seem like separate improvements. Patch by me, inspired by a much larger patch from Amit Kapila. Reviewed by Andres Freund. |
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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/.