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Re: Column Filtering in Logical Replication

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: vignesh C <vignesh21@gmail.com>, Rahila Syed <rahilasyed90@gmail.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Peter Smith <smithpb2250@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2021-09-28T03:29:51Z
Lists: pgsql-hackers 
On Mon, Sep 27, 2021 at 5:53 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
>
> On 2021-Sep-27, Amit Kapila wrote:
>
> > I am not sure what makes you say that we can't distinguish the above
> > cases when there is already a separate rule for CURRENT_SCHEMA? I
> > think you can distinguish by tracking the previous objects as we are
> > already doing in the patch. But one thing that is not clear to me is
> > is the reason to introduce a new type PUBLICATIONOBJ_CURRSCHEMA when
> > we use PUBLICATIONOBJ_REL_IN_SCHEMA and PUBLICATIONOBJ_CONTINUATION to
> > distinguish all cases of CURRENT_SCHEMA. Alvaro might have something
> > in mind for this which is not apparent and that might have caused
> > confusion to you as well?
>
> My issue is what happens if you have a schema that is named
> CURRENT_SCHEMA.  In the normal case where you do ALL TABLES IN SCHEMA
> "CURRENT_SCHEMA" you would end up with a String containing
> "CURRENT_SCHEMA", so how do you distinguish that from ALL TABLES IN
> SCHEMA CURRENT_SCHEMA, which does not refer to the schema named
> "CURRENT_SCHEMA" but in Vignesh's proposal also uses a String containing
> "CURRENT_SCHEMA"?
>
> Now you could say "but who would be stupid enough to do that??!",
>

But it is not allowed to create schema or table with the name
CURRENT_SCHEMA, so not sure if we need to do anything special for it.
However, if we want to handle it as a separate enum then the handling
would be something like:

| ALL TABLES IN_P SCHEMA CURRENT_SCHEMA
                                        {
                                                $$ =
makeNode(PublicationObjSpec);
                                                $$->pubobjtype =
PUBLICATIONOBJ_CURRSCHEMA;
                                        }
...
...
| CURRENT_SCHEMA
                                        {
                                                $$ =
makeNode(PublicationObjSpec);
                                                $$->pubobjtype =
PUBLICATIONOBJ_CONTINUATION;
                                        }
                ;

Now, during post-processing, the PUBLICATIONOBJ_CONTINUATION will be
distinguished as CURRENT_SCHEMA because both rangeVar and name will be
NULL. Do you have other ideas to deal with it? Vignesh has already
point in his email [1] why we can't keep pubobjtype as
PUBLICATIONOBJ_CURRSCHEMA in the second case, so I used
PUBLICATIONOBJ_CONTINUATION.

[1] - https://www.postgresql.org/message-id/CALDaNm06shp%2BALwC2s-dV-S4k2o6bcmXnXGX4ETkoXxKHQfjfA%40mail.gmail.com

-- 
With Regards,
Amit Kapila.

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Doc: Explain about Column List feature.

  2. Doc: fix column list vs. replica identity rules.

  3. Prohibit combining publications with different column lists.

  4. Fix the check to limit sync workers.

  5. Wait for subscription to sync in t/031_column_list.sql

  6. Move prattrs to the pg_publication_rel section in docs

  7. Allow specifying column lists for logical replication

  8. Fix row filters with multiple publications

  9. Fix publish_as_relid with multiple publications

  10. Add some additional tests for row filters in logical replication.

  11. Add index on pg_publication_rel.prpubid

  12. Avoid using DefElemAction in AlterPublicationStmt

  13. Small cleanups related to PUBLICATION framework code

  14. Add PublicationTable and PublicationRelInfo structs

  15. Fix various concurrency issues in logical replication worker launching