mirror of
https://github.com/postgres/postgres.git
synced 2025-05-20 00:03:14 -04:00
48354581a4
Pinning/Unpinning a buffer is a very frequent operation; especially in read-mostly cache resident workloads. Benchmarking shows that in various scenarios the spinlock protecting a buffer header's state becomes a significant bottleneck. The problem can be reproduced with pgbench -S on larger machines, but can be considerably worse for queries which touch the same buffers over and over at a high frequency (e.g. nested loops over a small inner table). To allow atomic operations to be used, cram BufferDesc's flags, usage_count, buf_hdr_lock, refcount into a single 32bit atomic variable; that allows to manipulate them together using 32bit compare-and-swap operations. This requires reducing MAX_BACKENDS to 2^18-1 (which could be lifted by using a 64bit field, but it's not a realistic configuration atm). As not all operations can easily implemented in a lockfree manner, implement the previous buf_hdr_lock via a flag bit in the atomic variable. That way we can continue to lock the header in places where it's needed, but can get away without acquiring it in the more frequent hot-paths. There's some additional operations which can be done without the lock, but aren't in this patch; but the most important places are covered. As bufmgr.c now essentially re-implements spinlocks, abstract the delay logic from s_lock.c into something more generic. It now has already two users, and more are coming up; there's a follupw patch for lwlock.c at least. This patch is based on a proof-of-concept written by me, which Alexander Korotkov made into a fully working patch; the committed version is again revised by me. Benchmarking and testing has, amongst others, been provided by Dilip Kumar, Alexander Korotkov, Robert Haas. On a large x86 system improvements for readonly pgbench, with a high client count, of a factor of 8 have been observed. Author: Alexander Korotkov and Andres Freund Discussion: 2400449.GjM57CE0Yg@dinodell
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/.