RE: row filtering for logical replication

On Tues, Nov 23, 2021 6:16 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Tue, Nov 23, 2021 at 1:29 PM houzj(dot)fnst(at)fujitsu(dot)com
> <houzj(dot)fnst(at)fujitsu(dot)com> wrote:
> >
> > On Tues, Nov 23, 2021 2:27 PM vignesh C <vignesh21(at)gmail(dot)com> wrote:
> > > On Thu, Nov 18, 2021 at 7:04 AM Peter Smith <smithpb2250(at)gmail(dot)com>
> > > wrote:
> > > >
> > > > PSA new set of v40* patches.
> > >
> > > Few comments:
> > > 1) When a table is added to the publication, replica identity is checked. But
> > > while modifying the publish action to include delete/update, replica identity is
> > > not checked for the existing tables. I felt it should be checked for the existing
> > > tables too.
> >
> > In addition to this, I think we might also need some check to prevent user from
> > changing the REPLICA IDENTITY index which is used in the filter expression.
> >
> > I was thinking is it possible do the check related to REPLICA IDENTITY in
> > function CheckCmdReplicaIdentity() or In GetRelationPublicationActions(). If we
> > move the REPLICA IDENTITY check to this function, it would be consistent with
> > the existing behavior about the check related to REPLICA IDENTITY(see the
> > comments in CheckCmdReplicaIdentity) and seems can cover all the cases
> > mentioned above.
> >
>
> Yeah, adding the replica identity check in CheckCmdReplicaIdentity()
> would cover all the above cases but I think that would put a premium
> on each update/delete operation. I think traversing the expression
> tree (it could be multiple traversals if the relation is part of
> multiple publications) during each update/delete would be costly.
> Don't you think so?

Yes, I agreed that traversing the expression every time would be costly.

I thought maybe we can cache the columns used in row filter or cache only the a
flag(can_update|delete) in the relcache. I think every operation that affect
the row-filter or replica-identity will invalidate the relcache and the cost of
check seems acceptable with the cache.

The reason that I thought it might be better do check in
CheckCmdReplicaIdentity is that we might need to add duplicate check code for
a couple of places otherwise, for example, we might need to check
replica-identity when:

[ALTER REPLICA IDENTITY |
DROP INDEX |
ALTER PUBLICATION ADD TABLE |
ALTER PUBLICATION SET (pubaction)]

Best regards,
Hou zj