Hi!
The same script was run, but using vacuum verbose analyze, and I saw the
difference again in the fifth step:
with your patch: buffer usage: 32312 hits, 607 misses, 1566 dirtied
master: buffer usage: 32346 hits, 573 misses, 1360 dirtied
Isn't there a chance for the checkpointer to run during this time? That could
make the conditions between the two runs slightly different and explain the
change in buffer report.
[0]https://github.com/postgres/postgres/blob/8a1b31e6e59631807a08a4e9465134c343bbdf5e/src/backend/access/heap/vacuumlazy.c#L2826-L2831
Looking at the script, you won't trigger the problem.
Thank you for the link I accounted it in my next experiments.
I repeated the test without processing checkpoints with a single index, and the
number of pages in the buffer used almost matched:
master branch: buffer usage: 32315 hits, 606 misses, 4486 dirtied
with applied patch v4 version: buffer usage: 32315 hits, 606 misses, 4489
dirtied
I think you are right - the problem was interfering with the checkpoint
process, by the way I checked the first version patch. To cut a long story
short, everything is fine now with one index.
Just in case, I'll explain: I considered this case because your patch could
have impact influenced it too.
On 25.04.2024 10:17, Anthonin Bonnefoy wrote:
On Wed, Apr 24, 2024 at 4:01 PM Alena Rybakina<lena.riback...@yandex.ru> wrote:
I tested the main postgres branch with and without your fix using a script that
was written by me. It consists of five scenarios and I made a comparison in the
logs between the original version of the master branch and the master branch
with your patch:
Hi! Thanks for the tests.
I have attached a test file (vacuum_check_logs.sql)
The reporting issue will only happen if there's a parallel index vacuum and it
will only happen if there's at least 2 indexes [0]. You will need to create an
additional index.
Speaking of the problem, I added another index and repeated the test and found
a significant difference:
I found it when I commited the transaction (3):
master: 2964 hits, 0 misses, 0 dirtied
with applied patch v4 version: buffer usage: 33013 hits, 0 misses, 3 dirtied
When I deleted all the data from the table and later started vacuum verbose
again (4):
master: buffer usage: 51486 hits, 0 misses, 0 dirtied
with applied patch v4 version:buffer usage: 77924 hits, 0 misses, 0 dirtied
when I inserted 1 million data into the table and updated it (5):
master:buffer usage: 27904 hits, 5021 misses, 1777 dirtied
with applied patch v4 version:buffer usage: 41051 hits, 9973 misses, 2564
dirtied
As I see, the number of pages is significantly more than it was in the master
branch and ,frankly, I couldn't fully figure out if it was a mistake or not.
