Horton

Re: Replication slot stats misgivings

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Andres Freund <andres@anarazel.de>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Date: 2021-05-11T22:29:59Z
Lists: pgsql-hackers

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On Wed, May 12, 2021 at 6:32 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Amit Kapila <amit.kapila16@gmail.com> writes:
> > I have closed this open item.
>
> That seems a little premature, considering that the
> contrib/test_decoding/sql/stats.sql test case is still failing regularly.

Thank you for reporting.

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.

For the record, during streaming transactions, IIUC this kind of thing
doesn’t happen since we update both total_bytes/txns and
stream_bytes/txns before reporting slot stats.

I've attached a patch to fix it.

Regards,


--
Masahiko Sawada
EDB:  https://www.enterprisedb.com/

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.