Horton

Re: Replication slot stats misgivings

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Andres Freund <andres@anarazel.de>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Date: 2021-05-12T03:37:50Z
Lists: pgsql-hackers 
On Wed, May 12, 2021 at 7:53 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, May 12, 2021 at 4:00 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > Ugh, since by commit 592f00f8de we send slot stats every after
> > spil/stream it’s possible that we report slot stats that have non-zero
> > counters for spill_bytes/txns and zeroes for total_bytes/txns. It
> > seems to me it’s legitimate that the slot stats view shows non-zero
> > values for spill_bytes/txns and zero values for total_bytes/txns
> > during decoding a large transaction. So I think we can fix the test
> > script so that it checks only spill_bytes/txns when checking spilled
> > transactions.
> >
>
> Your analysis and fix look correct to me.
>

I think the part of the test that tests the stats after resetting it
might give different results. This can happen because in the previous
test we spill multiple times (spill_count is 12 in my testing) and it
is possible that some of the spill stats messages is received by stats
collector after the reset message. If this theory is correct then it
better that we remove the test for reset stats and the test after it
"decode and check stats again.". This is not directly related to your
patch or buildfarm failure but I guess this can happen and we might
see such a failure in future.

-- 
With Regards,
Amit Kapila.

Commits

  1. Doc: Update logical decoding stats information.

  2. Fix tests for replication slots stats.

  3. Update replication statistics after every stream/spill.

  4. Fix the computation of slot stats for 'total_bytes'.

  5. Another try to fix the test case added by commit f5fc2f5b23.

  6. Use HTAB for replication slot statistics.

  7. Fix test case added by commit f5fc2f5b23.

  8. Add information of total data processed to replication slot stats.

  9. Use NameData datatype for slotname in stats.