On Tue, Apr 19, 2022 at 4:36 PM Nathan Bossart <nathandboss...@gmail.com> wrote:
> On Tue, Apr 19, 2022 at 04:21:21PM -0700, David G. Johnston wrote: > > I've done this four times in a row and while the number of dirty buffers > > shown each time vary (see below) I see that "wrote N buffers" is always > > exactly one more than the total count of dirty buffers. I'm just curious > > if anyone has a quick answer for this unusual correspondence. > > I see that SlruInternalWritePage() increments ckpt_bufs_written, so my > first guess would be that it's due to something like CheckPointCLOG(). > > I peeked at pg_stat_bgwriter and see an increase in buffers_checkpoint matching the dirty buffers number. I also looked at pg_stat_slru to try and find the corresponding change caused by: slru.c:766 (SlruPhysicalWritePage) pgstat_count_slru_page_written(shared->slru_stats_idx); I do see (Xact) blks_hit change during this process (after the update/commit, not the checkpoint, though) but it increases by 2 when dirty buffers is 4. I was expecting 4, thinking that blocks and buffers and pages are basically the same things (which [1] seems to affirm). https://www.postgresql.org/message-id/13563.1044552279%40sss.pgh.pa.us David J.
