This commit adds "stats_reset" column into the pg_stat_statements_info
view. This column indicates the time at which all statistics in the
pg_stat_statements view were last reset.
Per discussion, this commit also changes pg_stat_statements_info code
so that "dealloc" column is reset at the same time as "stats_reset" is reset,
i.e., whenever all pg_stat_statements entries are removed, for the sake
of consistency. Previously "dealloc" was reset only when
pg_stat_statements_reset(0, 0, 0) is called and was not reset when
pg_stat_statements_reset() with non-zero value argument discards all
entries. This was confusing.
Author: Naoki Nakamichi, Yuki Seino
Reviewed-by: Yuki Seino, Kyotaro Horiguchi, Li Japin, Fujii Masao
Discussion: https://postgr.es/m/c102cf3180d0ee73c1c5a0f7f8558322@oss.nttdata.com
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
Magnus Hagander
Fujii Masao