Thread: pg_stat_bgwriter
Dear I would like to share with you to see what you think about the statistics of pg_stat_bgwriter postgres = # select * from pg_stat_bgwriter; checkpoints_timed | checkpoints_req | checkpoint_write_time | checkpoint_sync_time | buffers_checkpoint | buffers_clean | maxwritten_clean | buffers_backend | buffers_ backend_fsync | buffers_alloc | stats_reset ------------------- + ----------------- + ------------ ----------- + ---------------------- + --------------- ----- + --------------- + ------------------ + --------- -------- + --------- -------------- + --------------- + ------------------- ------------ 338 | 6 | 247061792 | 89418 | 2939561 | 19872289 | 54876 | 6015787 | 0 | 710682240 | 2019-10-06 19: 25: 30.688186-03 (1 row) postgres = # show bgwriter_delay; bgwriter_delay ---------------- 200ms (1 row) postgres = # show bgwriter_lru_maxpages; bgwriter_lru_maxpages ----------------------- 100 (1 row) postgres = # show bgwriter_lru_multiplier; bgwriter_lru_multiplier ------------------------- 2 (1 row) Do you think it should increase bgwriter_lru_maxpages due to the value of maxwritten_clean? Do you think it should increase bgwriter_lru_maxpages, bgwriter_lru_multiplier, and decrease bgwriter_delay due to the value of buffers_backend compared to buffers_alloc? Do you think a modification is necessary? What values would you recommend? thank you -- Sent from: https://www.postgresql-archive.org/PostgreSQL-performance-f2050081.html
On Mon, Oct 14, 2019 at 1:25 PM dangal <danielito.gallo@gmail.com> wrote:
Do you think it should increase bgwriter_lru_maxpages due to the value of
maxwritten_clean?
I find the background writer to be pretty unimportant these days. If the kernel is freely accepting writes without blocking, the backends can probably write their own buffers without it being a meaningful bottleneck. On the other hand, if the kernel is constipated, no tweaking of the background writer parameters is going to insulate the backends from that fact. That said, I would increase bgwriter_lru_maxpages (or decrease bgwriter_delay) anyway. It probably won't make much difference, but if it does it is more likely to help than to hurt.
Do you think it should increase bgwriter_lru_maxpages,
bgwriter_lru_multiplier, and decrease bgwriter_delay due to the value of
buffers_backend compared to buffers_alloc?
I don't think that that comparison is meaningful, so wouldn't make changes based on it.
Do you think a modification is necessary?
What values would you recommend?
thank you
If you are experiencing a problem, this is probably not the right way to investigate it. If a particular query is slow, try EXPLAIN (ANALYZE, BUFFERS). If lots of user-facing things are slow, try sampling "select wait_event, wait_event_type from pg_stat_activity where backend_type='client backend';"
thank you very much jeff I'll see with the team that manages the operating system to see if they can help me with this data that you have given me -- Sent from: https://www.postgresql-archive.org/PostgreSQL-performance-f2050081.html