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If more distinct statements than pg_stat_statements.max are observed, pg_stat_statements entries about the least-executed statements are deallocated. This commit enables us to track the total number of times those entries were deallocated. That number can be viewed in the pg_stat_statements_info view that this commit adds. It's useful when tuning pg_stat_statements.max parameter. If it's high, i.e., the entries are deallocated very frequently, which might cause the performance regression and we can increase pg_stat_statements.max to avoid those frequent deallocations. The pg_stat_statements_info view is intended to display the statistics of pg_stat_statements module itself. Currently it has only one column "dealloc" indicating the number of times entries were deallocated. But an upcoming patch will add other columns (for example, the time at which pg_stat_statements statistics were last reset) into the view. Author: Katsuragi Yuta, Yuki Seino Reviewed-by: Fujii Masao Discussion: https://postgr.es/m/0d9f1107772cf5c3f954e985464c7298@oss.nttdata.com
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/.