Re: Replication slot stats misgivings

On Tue, Mar 30, 2021 at 11:00 AM Andres Freund <andres(at)anarazel(dot)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(at)anarazel(dot)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