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After autovacuum collects the relations to vacuum or analyze, it rechecks whether each relation still needs to be vacuumed or analyzed before actually doing that. Previously this recheck could be a significant overhead especially when there were a very large number of relations. This was because each recheck forced the statistics to be refreshed, and the refresh of the statistics for a very large number of relations could cause heavy overhead. There was the report that this issue caused autovacuum workers to have gotten “stuck” in a tight loop of table_recheck_autovac() that rechecks whether a relation needs to be vacuumed or analyzed. This commit speeds up the recheck by making autovacuum worker reuse the previously-read statistics for the recheck if possible. Then if that "stale" statistics says that a relation still needs to be vacuumed or analyzed, autovacuum refreshes the statistics and does the recheck again. The benchmark shows that the more relations exist and autovacuum workers are running concurrently, the more this change reduces the autovacuum execution time. For example, when there are 20,000 tables and 10 autovacuum workers are running, the benchmark showed that the change improved the performance of autovacuum more than three times. On the other hand, even when there are only 1000 tables and only a single autovacuum worker is running, the benchmark didn't show any big performance regression by the change. Firstly POC patch was proposed by Jim Nasby. As the result of discussion, we used Tatsuhito Kasahara's version of the patch using the approach suggested by Tom Lane. Reported-by: Jim Nasby Author: Tatsuhito Kasahara Reviewed-by: Masahiko Sawada, Fujii Masao Discussion: https://postgr.es/m/3FC6C2F2-8A47-44C0-B997-28830B5716D0@amazon.com |
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| GNUmakefile.in | ||
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| README.git | ||
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README
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: https://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 https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.