Re: Replication slot stats misgivings

On Wed, May 12, 2021 at 4:00 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Wed, May 12, 2021 at 6:32 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> >
> > Amit Kapila <amit(dot)kapila16(at)gmail(dot)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.
>

Your analysis and fix look correct to me. I'll test and push your
patch if I don't see any problem with it.

> 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.
>

Right, because during streaming, we send the data to the decoding plugin.

--
With Regards,
Amit Kapila.