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When relations are dropped, at end of transaction we need to remove the files and clean the buffer pool of buffers containing pages of those relations. Previously we would scan the buffer pool once per relation to clean up buffers. When there are many relations to drop, the repeated scans make this process slow; so we now instead pass a list of relations to drop and scan the pool once, checking each buffer against the passed list. When the number of relations is larger than a threshold (which as of this patch is being set to 20 relations) we sort the array before starting, and bsearch the array; when it's smaller, we simply scan the array linearly each time, because that's faster. The exact optimal threshold value depends on many factors, but the difference is not likely to be significant enough to justify making it user-settable. This has been measured to be a significant win (a 15x win when dropping 100,000 relations; an extreme case, but reportedly a real one). Author: Tomas Vondra, some tweaks by me Reviewed by: Robert Haas, Shigeru Hanada, Andres Freund, Álvaro Herrera |
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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/.