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: vignesh C <vignesh21@gmail.com>, Andres Freund <andres@anarazel.de>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Date: 2021-04-28T09:39:00Z
Lists: pgsql-hackers 
On Wed, Apr 28, 2021 at 12:49 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
>
> BTW regarding the commit f5fc2f5b23 that added total_txns and
> total_bytes, we add the reorder buffer size (i.g., rb->size) to
> rb->totalBytes but I think we should use the transaction size (i.g.,
> txn->size) instead:
>

You are right about the problem but I think your proposed fix also
won't work because txn->size always has current transaction size which
will be top-transaction in the case when a transaction has multiple
subtransactions. It won't include the subtxn->size. For example, you
can try to decode with below kind of transaction:
Begin;
insert into t1 values(1);
savepoint s1;
insert into t1 values(2);
savepoint s2;
insert into t1 values(3);
commit;

I think we can fix it by keeping track of total_size in toptxn as we
are doing for the streaming case in ReorderBufferChangeMemoryUpdate.
We can probably do it for non-streaming cases as well.

-- 
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.