Re: row filtering for logical replication

On Tue, Nov 9, 2021 at 2:22 PM houzj(dot)fnst(at)fujitsu(dot)com
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> On Fri, Nov 5, 2021 4:49 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > On Fri, Nov 5, 2021 at 10:44 AM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
> > >
> > > PSA new set of v37* patches.
> > 3.
> > - | ColId
> > + | ColId OptWhereClause
> > {
> > $$ = makeNode(PublicationObjSpec);
> > $$->pubobjtype = PUBLICATIONOBJ_CONTINUATION;
> > - $$->name = $1;
> > + if ($2)
> > + {
> > + $$->pubtable = makeNode(PublicationTable); $$->pubtable->relation =
> > + makeRangeVar(NULL, $1, @1); $$->pubtable->whereClause = $2; } else {
> > + $$->name = $1; }
> >
> > Again this doesn't appear to be the right way. I think this should be handled at
> > a later point.
>
> I think the difficulty to handle this at a later point is that we need to make
> sure we don't lose the whereclause. Currently, we can only save the whereclause
> in PublicationTable structure and the PublicationTable is only used for TABLE,
> but '| ColId' can be used for either a SCHEMA or TABLE. We cannot distinguish
> the actual type at this stage, so we always need to save the whereclause if
> it's NOT NULL.
>

I see your point. But, I think we can add some comments here
indicating that the user might have mistakenly given where clause with
some schema which we will identify later and give an appropriate
error. Then, in preprocess_pubobj_list(), identify if the user has
given the where clause with schema name and give an appropriate error.

> I think the possible approaches to delay this check are:
>
> (1) we can delete the PublicationTable structure and put all the vars(relation,
> whereclause) in PublicationObjSpec. In this approach, we don't need check if
> the whereclause is NULL in the '| ColId', we can check this at a later point.
>

Yeah, we can do this but I don't think it will reduce any checks later
to identify if the user has given where clause only for tables. So,
let's keep this structure around as that will at least keep all things
related to the table together in one structure.

> Or
>
> (2) Add a new pattern for whereclause in PublicationObjSpec:
>
> The change could be:
>
> PublicationObjSpec:
> ...
> | ColId
> ...
> + | ColId WHERE '(' a_expr ')'
> + {
> + $$ = makeNode(PublicationObjSpec);
> + $$->pubobjtype = PUBLICATIONOBJ_CONTINUATION;
> + $$->pubtable = makeNode(PublicationTable);
> + $$->pubtable->relation = makeRangeVar(NULL, $1, @1);
> + $$->pubtable->whereClause = $2;
> + }
>
> In this approach, we also don't need the "if ($2)" check.
>

This seems redundant and we still need same checks later to see if the
where clause is given with the table object.

--
With Regards,
Amit Kapila.