Horton

Re: row filtering for logical replication

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Greg Nancarrow <gregn4422@gmail.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, vignesh C <vignesh21@gmail.com>, Peter Smith <smithpb2250@gmail.com>, "tanghy.fnst@fujitsu.com" <tanghy.fnst@fujitsu.com>, Ajin Cherian <itsajin@gmail.com>, Euler Taveira <euler@eulerto.com>, Rahila Syed <rahilasyed90@gmail.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>, Önder Kalacı <onderkalaci@gmail.com>, japin <japinli@hotmail.com>, Michael Paquier <michael@paquier.xyz>, David Steele <david@pgmasters.net>, Craig Ringer <craig@2ndquadrant.com>, Amit Langote <amitlangote09@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-11-29T11:06:06Z
Lists: pgsql-hackers

Commits

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

  1. Release cache tuple when no longer needed

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

  3. Fix one of the tests introduced in commit 52e4f0cd47.

  4. Allow specifying row filters for logical replication of tables.

  5. Move scanint8() to numutils.c

  6. Replace Test::More plans with done_testing

  7. Reduce relcache access in WAL sender streaming logical changes

  8. Small cleanups related to PUBLICATION framework code

  9. Add a view to show the stats of subscription workers.

  10. Allow publishing the tables of schema.

  11. Doc: improve documentation of CREATE/ALTER SUBSCRIPTION.

  12. Add PublicationTable and PublicationRelInfo structs

  13. Remove unused argument "txn" in maybe_send_schema().

  14. Add prepare API support for streaming transactions in logical replication.

  15. Unify PostgresNode's new() and get_new_node() methods

  16. Use l*_node() family of functions where appropriate

  17. Add support for prepared transactions to built-in logical replication.

  18. Restore the portal-level snapshot after procedure COMMIT/ROLLBACK.

  19. Rename a parse node to be more general

  20. Remove unused column atttypmod from initial tablesync query

  21. SEARCH and CYCLE clauses

On Mon, Nov 29, 2021 at 3:41 PM Amit Kapila <amit.kapila16@gmail.com> wrote:

> > ---- Publisher:
> > INSERT INTO tbl1 VALUES (1,1);
> > UPDATE tbl1 SET a = 2;
> >
> > Prior to the UPDATE above:
> > On pub side, tbl1 contains (1,1).
> > On sub side, tbl1 contains (1,1)
> >
> > After the above UPDATE:
> > On pub side, tbl1 contains (2,1).
> > On sub side, tbl1 contains (1,1), (2,1)
> >
> > So the UPDATE on the pub side has resulted in an INSERT of (2,1) on
> > the sub side.
> >
> > This is because when (1,1) is UPDATEd to (2,1), it attempts to use the
> > "insert" filter "(b<2)" to determine whether the old value had been
> > inserted (published to subscriber), but finds there is no "b" value
> > (because it only uses RI cols for UPDATE) and so has to assume the old
> > tuple doesn't exist on the subscriber, hence the UPDATE ends up doing
> > an INSERT.
> > INow if the use of RI cols were enforced for the insert filter case,
> > we'd properly know the answer as to whether the old row value had been
> > published and it would have correctly performed an UPDATE instead of
> > an INSERT in this case.
> >
>
> I don't think it is a good idea to combine the row-filter from the
> publication that publishes just 'insert' with the row-filter that
> publishes 'updates'. We shouldn't apply the 'insert' filter for
> 'update' and similarly for publication operations. We can combine the
> filters when the published operations are the same. So, this means
> that we might need to cache multiple row-filters but I think that is
> better than having another restriction that publish operation 'insert'
> should also honor RI columns restriction.

I am just wondering that if we don't combine filter in the above case
then what data we will send to the subscriber if the operation is
"UPDATE tbl1 SET a = 2, b=3", so in this case, we will apply only the
update filter i.e. a > 1 so as per that this will become the INSERT
operation because the old row was not passing the filter.  So now we
will insert a new row in the subscriber-side with value (2,3).  Looks
a bit odd to me that the value b=3 would have been rejected with the
direct insert but it is allowed due to indirect insert done by update.
Is this behavior looks odd only to me?

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com