Re: Skip collecting decoded changes of already-aborted transactions

On Mon, 3 Jul 2023 at 07:16, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Fri, Jun 23, 2023 at 12:39 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> >
> > On Fri, Jun 9, 2023 at 10:47 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > >
> > > Hi,
> > >
> > > In logical decoding, we don't need to collect decoded changes of
> > > aborted transactions. While streaming changes, we can detect
> > > concurrent abort of the (sub)transaction but there is no mechanism to
> > > skip decoding changes of transactions that are known to already be
> > > aborted. With the attached WIP patch, we check CLOG when decoding the
> > > transaction for the first time. If it's already known to be aborted,
> > > we skip collecting decoded changes of such transactions. That way,
> > > when the logical replication is behind or restarts, we don't need to
> > > decode large transactions that already aborted, which helps improve
> > > the decoding performance.
> > >
> > +1 for the idea of checking the transaction status only when we need
> > to flush it to the disk or send it downstream (if streaming in
> > progress is enabled). Although this check is costly since we are
> > planning only for large transactions then it is worth it if we can
> > occasionally avoid disk or network I/O for the aborted transactions.
> >
>
> Thanks.
>
> I've attached the updated patch. With this patch, we check the
> transaction status for only large-transactions when eviction. For
> regression test purposes, I disable this transaction status check when
> logical_replication_mode is set to 'immediate'.

May be there is some changes that are missing in the patch, which is
giving the following errors:
reorderbuffer.c: In function ‘ReorderBufferCheckTXNAbort’:
reorderbuffer.c:3584:22: error: ‘logical_replication_mode’ undeclared
(first use in this function)
3584 | if (unlikely(logical_replication_mode ==
LOGICAL_REP_MODE_IMMEDIATE))
| ^~~~~~~~~~~~~~~~~~~~~~~~

Regards,
Vignesh