Re: Skipping logical replication transactions on subscriber side

On Wed, Jan 12, 2022 at 12:21 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Wed, Jan 12, 2022 at 5:49 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> >
> > On Tue, Jan 11, 2022 at 7:08 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > > On Tue, Jan 11, 2022 at 1:51 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
> > > >
> > > > On second thought, the same is true for other cases, for example,
> > > > preparing the transaction and clearing skip_xid while handling a
> > > > prepare message. That is, currently we don't clear skip_xid while
> > > > handling a prepare message but do that while handling commit/rollback
> > > > prepared message, in order to avoid the worst case. If we do both
> > > > while handling a prepare message and the server crashes between them,
> > > > it ends up that skip_xid is cleared and the transaction will be
> > > > resent, which is identical to the worst-case above.
> > > >
> > >
> > > How are you thinking to update the skip xid before prepare? If we do
> > > it in the same transaction then the changes in the catalog will be
> > > part of the prepared xact but won't be committed. Now, say if we do it
> > > after prepare, then the situation won't be the same because after
> > > restart the same xact won't appear again.
> >
> > I was thinking to commit the catalog change first in a separate
> > transaction while not updating origin LSN and then prepare an empty
> > transaction while updating origin LSN.
> >
>
> But, won't it complicate the handling if in the future we try to
> enhance this API such that it skips partial changes like skipping only
> for particular relation(s) or particular operations as discussed
> previously in this thread?

Right. I was thinking that if we accept the situation that the user
has to set skip_xid again in case of the server crashes, we might be
able to accept also the situation that the user has to clear skip_xid
in a case of the server crashes. But it seems the former is less
problematic.

I've attached an updated patch that incorporated all comments I got so far.

Regards,

--
Masahiko Sawada
EDB: https://www.enterprisedb.com/