Re: row filtering for logical replication

On Thu, Jan 20, 2022 at 6:43 PM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
>
> And the actual reason I was looking at this code, is that I had stumbled
> upon the new GetRelationPublicationInfo() function, which has an even
> weirder API:
>
> > * Get the publication information for the given relation.
> > *
> > * Traverse all the publications which the relation is in to get the
> > * publication actions and validate the row filter expressions for such
> > * publications if any. We consider the row filter expression as invalid if it
> > * references any column which is not part of REPLICA IDENTITY.
> > *
> > * To avoid fetching the publication information, we cache the publication
> > * actions and row filter validation information.
> > *
> > * Returns the column number of an invalid column referenced in a row filter
> > * expression if any, InvalidAttrNumber otherwise.
> > */
> > AttrNumber
> > GetRelationPublicationInfo(Relation relation, bool validate_rowfilter)
>
> "Returns *an* invalid column referenced in a RF if any"? That sounds
> very strange. And exactly what info is it getting, given that there is
> no actual returned info?
>

It returns an invalid column referenced in an RF if any but if not
then it helps to form pubactions which is anyway required at a later
point in the caller. The idea is that when we are already traversing
publications we should store/gather as much info as possible. I think
probably the API name is misleading, maybe we should name it something
like ValidateAndFetchPubInfo, ValidateAndRememberPubInfo, or something
along these lines?

> Maybe this was meant to be "validate RF
> expressions" and return, perhaps, a bitmapset of all invalid columns
> referenced?
>

Currently, we stop as soon as we find the first invalid column.

> (What is an invalid column in the first place?)
>

A column that is referenced in the row filter but is not part of
Replica Identity.

--
With Regards,
Amit Kapila.