RE: logical replication empty transactions

On Friday, February 18, 2022 6:18 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Tue, Feb 8, 2022 at 5:27 AM osumi(dot)takamichi(at)fujitsu(dot)com
> <osumi(dot)takamichi(at)fujitsu(dot)com> wrote:
> >
> > On Friday, August 13, 2021 8:01 PM Ajin Cherian <itsajin(at)gmail(dot)com> wrote:
> > > On Mon, Aug 2, 2021 at 7:20 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
> > > wrote:
> > Changing the timing to send the keepalive to the decoding commit
> > timing didn't look impossible to me, although my suggestion can be
> > ad-hoc.
> >
> > After the initialization of sentPtr(by confirmed_flush lsn), sentPtr
> > is updated from logical_decoding_ctx->reader->EndRecPtr in
> XLogSendLogical.
> > In the XLogSendLogical, we update it after we execute
> LogicalDecodingProcessRecord.
> > This order leads to the current implementation to wait the next
> > iteration to send a keepalive in WalSndWaitForWal.
> >
> > But, I felt we can utilize end_lsn passed to ReorderBufferCommit for
> > updating sentPtr. The end_lsn is the lsn same as the
> > ctx->reader->EndRecPtr, which means advancing the timing to update the
> sentPtr for the commit case.
> > Then if the transaction is empty in synchronous mode, send the
> > keepalive in WalSndUpdateProgress directly, instead of having the
> > force_keepalive_syncrep flag and having it true.
> >
>
> You have a point in that we don't need to delay sending this message till next
> WalSndWaitForWal() but I don't see why we need to change anything about
> update of sentPtr.
Yeah, you're right.
Now I think we don't need the update of sentPtr to send a keepalive.

I thought we can send a keepalive message
after its update in XLogSendLogical or any appropriate place for it after the existing update.

Best Regards,
Takamichi Osumi