Horton

Re: Replication slot stats misgivings

vignesh C <vignesh21@gmail.com>

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From: vignesh C <vignesh21@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Date: 2021-03-31T06:02:51Z
Lists: pgsql-hackers

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On Tue, Mar 30, 2021 at 11:00 AM Andres Freund <andres@anarazel.de> wrote:
>
> Hi,
>
> On 2021-03-30 10:13:29 +0530, vignesh C wrote:
> > On Tue, Mar 30, 2021 at 6:28 AM Andres Freund <andres@anarazel.de> wrote:
> > > Any chance you could write a tap test exercising a few of these cases?
> >
> > I can try to write a patch for this if nobody objects.
>
> Cool!
>

Attached a patch which has the test for the first scenario.

> > > E.g. things like:
> > >
> > > - create a few slots, drop one of them, shut down, start up, verify
> > >   stats are still sane
> > > - create a few slots, shut down, manually remove a slot, lower
> > >   max_replication_slots, start up
> >
> > Here by "manually remove a slot", do you mean to remove the slot
> > manually from the pg_replslot folder?
>
> Yep - thereby allowing max_replication_slots after the shutdown/start to
> be lower than the number of slots-stats objects.

I have not included the 2nd test in the patch as the test fails with
following warnings and also displays the statistics of the removed
slot:
WARNING:  problem in alloc set Statistics snapshot: detected write
past chunk end in block 0x55d038b8e410, chunk 0x55d038b8e438
WARNING:  problem in alloc set Statistics snapshot: detected write
past chunk end in block 0x55d038b8e410, chunk 0x55d038b8e438

This happens because the statistics file has an additional slot
present even though the replication slot was removed.  I felt this
issue should be fixed. I will try to fix this issue and send the
second test along with the fix.

Regards,
Vignesh

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.