Hello,
On one particular PG12.3 instance (same behaviour with PG12.4) we are experimenting occasional strange values in the
abovetables.
For instance looping (10s. period) over this request:
SELECT current_timestamp, checkpoints_timed,
checkpoints_req,
checkpoint_write_time,
checkpoint_sync_time,
buffers_checkpoint,
buffers_clean,
maxwritten_clean,
buffers_backend,
buffers_backend_fsync,
buffers_alloc
FROM pg_stat_bgwriter
Gives:
020-09-16 13:41:39.781609+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:41:49.815612+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:41:59.851812+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:42:09.89053+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:42:19.923291+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:42:29.959282+00,3291,227,1278516493,26327,66708986,1743379,16800,253585756,0,59080296
2020-09-16 13:42:39.98198+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:42:50.028727+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:43:00.067928+00,3291,227,1278516493,26327,66709285,1743379,16800,253585756,0,59080296
2020-09-16 13:43:10.090266+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:43:20.140272+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:43:30.170372+00,3291,227,1278516493,26327,66709585,1743379,16800,253585756,0,59080296
2020-09-16 13:43:40.204747+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:43:50.239374+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:44:00.26905+00,3291,227,1278516493,26327,66709884,1743379,16800,253585756,0,59080296
2020-09-16 13:44:10.314927+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:44:20.351091+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:44:30.408797+00,3291,227,1278516493,26327,66710184,1743379,16800,253585756,0,59080296
2020-09-16 13:44:40.44833+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
2020-09-16 13:44:50.484298+00,438,2,10095976,0,611207,870625,8695,612255,0,39028850
One can see that some columns that are supposed to increase only are not always. For instance checkpoints_timed
suddenlyjumps from 438 to 3291, then back to 438.
We experiment the same issue in pg_stat_database.
Thanks