Hi, On Fri, 10 May 2024 at 16:21, Nazir Bilal Yavuz <byavu...@gmail.com> wrote: > > Hi, > > On Fri, 10 May 2024 at 14:49, Alena Rybakina <lena.riback...@yandex.ru> wrote: > > > > Hi! I could try to check it with the test, but I want to ask you about > > details, because I'm not sure that I completely understand the test case. > > > > You mean that we need to have two backends and on one of them we deleted > > the tuples before vacuum called the other, do you? > > > > I think triggering a parallel vacuum is enough. I am able to see the > differences with the following: > > You can apply the attached diff file to see the differences between > the previous version and the patched version. Then, run this query: > > CREATE TABLE vacuum_fix (aid int, bid int, cid int) with > (autovacuum_enabled=false); > INSERT INTO vacuum_fix SELECT *, *, * FROM generate_series(1, 1000000); > CREATE INDEX a_idx on vacuum_fix (aid); > CREATE INDEX b_idx on vacuum_fix (bid); > CREATE INDEX c_idx on vacuum_fix (cid); > VACUUM vacuum_fix; > UPDATE vacuum_fix SET aid = aid + 1; > VACUUM (VERBOSE, PARALLEL 2) vacuum_fix ; > > After that I saw: > > INFO: vacuuming "test.public.vacuum_fix" > INFO: launched 2 parallel vacuum workers for index vacuuming (planned: 2) > INFO: finished vacuuming "test.public.vacuum_fix": index scans: 1 > ... > ... > buffer usage: 29343 hits, 9580 misses in the previous version, 14165 > misses in the patched version, 14262 dirtied > > Patched version counts 14165 misses but the previous version counts > 9580 misses in this specific example.
I am sorry that I showed the wrong thing, this is exactly what is fixed in this patch. Actually, I do not know how to trigger it; currently I am looking for it. I will share if anything comes to my mind. -- Regards, Nazir Bilal Yavuz Microsoft
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 49637284f91..a6f1df11066 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1355,6 +1355,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) IOContext io_context; IOObject io_object; char persistence; + static int double_counts = 0; /* * Currently operations are only allowed to include a read of some range, @@ -1426,6 +1427,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) operation->smgr->smgr_rlocator.locator.relNumber, operation->smgr->smgr_rlocator.backend, true); + double_counts++; continue; } @@ -1523,6 +1525,7 @@ WaitReadBuffers(ReadBuffersOperation *operation) if (VacuumCostActive) VacuumCostBalance += VacuumCostPageMiss * io_buffers_len; } + elog(LOG, "Double counts = %d", double_counts); } /*
