RE: [Patch] Optimize dropping of relation buffers using dlist

On Sunday, January 3, 2021 10:35 PM (JST), Amit Kapila wrote:
> On Sat, Jan 2, 2021 at 7:47 PM k(dot)jamison(at)fujitsu(dot)com
> <k(dot)jamison(at)fujitsu(dot)com> wrote:
> >
> > Happy new year. The V38 LGTM.
> > Apologies for a bit of delay on posting the test results, but since
> > it's the start of commitfest, here it goes and the results were interesting.
> >
> > I executed a VACUUM test using the same approach that Tsunakawa-san
> > did in [1], but only this time, the total time that DropRelFileNodeBuffers()
> took.
> >
>
> Please specify the exact steps like did you deleted all the rows from a table or
> some of it or none before performing Vacuum? How did you measure this
> time, did you removed the cached check? It would be better if you share the
> scripts and or the exact steps so that the same can be used by others to
> reproduce.

Basically, I used the TimestampDifference function in DropRelFileNodeBuffers().
I also executed DELETE before VACUUM.
I also removed nBlocksToInvalidate < BUF_DROP_FULL_SCAN_THRESHOLD
And used the threshold as the relation size.

> Hmm, in the tests done by Tang, the results indicate that in some cases the
> patched version is slower at even NBuffers/32, so not sure if we can go to
> values shown by you unless she is doing something wrong. I think the
> difference in results could be because both of you are using different
> techniques to measure the timings, so it might be better if both of you can
> share scripts or exact steps used to measure the time and other can use the
> same technique and see if we are getting consistent results.

Right, since we want consistent results, please disregard the approach that I did.
I will resume the test similar to Tang, because she also executed the original failover
test which I have been doing before.
To avoid confusion and to check if the results from mine and Tang are consistent,
I also did the recovery/failover test for VACUUM on single relation, which I will send
in a separate email after this.

Regards,
Kirk Jamison