Horton

RE: row filtering for logical replication

Zhijie Hou (Fujitsu) <houzj.fnst@fujitsu.com>

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From: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: vignesh C <vignesh21@gmail.com>, Peter Smith <smithpb2250@gmail.com>, Greg Nancarrow <gregn4422@gmail.com>, "tanghy.fnst@fujitsu.com" <tanghy.fnst@fujitsu.com>, Ajin Cherian <itsajin@gmail.com>, Dilip Kumar <dilipbalaut@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: 2021-11-25T13:39:45Z
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 Wed, Nov 24, 2021 1:46 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> On Wed, Nov 24, 2021 at 6:51 AM houzj.fnst@fujitsu.com
> <houzj.fnst@fujitsu.com> wrote:
> >
> > On Tues, Nov 23, 2021 6:16 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > > On Tue, Nov 23, 2021 at 1:29 PM houzj.fnst@fujitsu.com
> > > <houzj.fnst@fujitsu.com> wrote:
> > > >
> > > > On Tues, Nov 23, 2021 2:27 PM vignesh C <vignesh21@gmail.com> wrote:
> > > > > On Thu, Nov 18, 2021 at 7:04 AM Peter Smith
> > > > > <smithpb2250@gmail.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.
> >
> 
> I think if we can cache this information especially as a bool flag then that should
> probably be better.

When researching and writing a top-up patch about this.
I found a possible issue which I'd like to confirm first.

It's possible the table is published in two publications A and B, publication A
only publish "insert" , publication B publish "update". When UPDATE, both row
filter in A and B will be executed. Is this behavior expected?

For example:
---- Publication
create table tbl1 (a int primary key, b int);
create publication A for table tbl1 where (b<2) with(publish='insert');
create publication B for table tbl1 where (a>1) with(publish='update');

---- Subscription
create table tbl1 (a int primary key);
CREATE SUBSCRIPTION sub CONNECTION 'dbname=postgres host=localhost
port=10000' PUBLICATION A,B;

---- Publication
update tbl1 set a = 2;

The publication can be created, and when UPDATE, the rowfilter in A (b<2) will
also been executed but the column in it is not part of replica identity.
(I am not against this behavior just confirm)

Best regards,
Hou zj