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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
The PostgreSQL contrib tree
---------------------------
This subtree contains porting tools, analysis utilities, and plug-in
features that are not part of the core PostgreSQL system, mainly
because they address a limited audience or are too experimental to be
part of the main source tree. This does not preclude their
usefulness.
User documentation for each module appears in the main SGML
documentation.
When building from the source distribution, these modules are not
built automatically, unless you build the "world" target. You can
also build and install them all by running "make all" and "make
install" in this directory; or to build and install just one selected
module, do the same in that module's subdirectory.
Some directories supply new user-defined functions, operators, or
types. To make use of one of these modules, after you have installed
the code you need to register the new SQL objects in the database
system by executing a CREATE EXTENSION command. In a fresh database,
you can simply do
CREATE EXTENSION module_name;
See the PostgreSQL documentation for more information about this
procedure.