Horton

Re: row filtering for logical replication

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Amit Kapila <amit.kapila16@gmail.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Euler Taveira <euler@eulerto.com>, Greg Nancarrow <gregn4422@gmail.com>, Peter Smith <smithpb2250@gmail.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>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Amit Langote <amitlangote09@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2021-07-13T15:44:43Z
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 Tue, 2021-07-13 at 10:24 +0530, Amit Kapila wrote:
> to do. AFAIU, the main things we want to prohibit in the filter are:
> (a) it doesn't refer to any relation other than catalog in where
> clause,

Right, because the walsender is using a historical snapshot.

> (b) it doesn't use UDFs in any way (in expressions, in
> user-defined operators, user-defined types, etc.),

Is this a reasonable requirement? Postgres has a long history of
allowing UDFs nearly everywhere that a built-in is allowed. It feels
wrong to make built-ins special for this feature.

> (c) the columns
> referred to in the filter should be part of PK or Replica Identity.

Why?


Also:

* Andres also mentioned that the function should not leak memory.
* One use case for this feature is when sharding a table, so the
expression should allow things like "hashint8(x) between ...". I'd
really like to see this problem solved, as well.

> I think in the long run one idea to allow UDFs is probably by
> explicitly allowing users to specify whether the function is
> publication predicate safe and if so, then we can allow such
> functions
> in the filter clause.

This sounds like a better direction. We probably need some kind of
catalog information here to say what functions/operators are "safe" for
this kind of purpose. There are a couple questions:

1. Should this notion of safety be specific to this feature, or should
we try to generalize it so that other areas of the system might benefit
as well?

2. Should this marking be superuser-only, or user-specified?

3. Should it be related to the IMMUTABLE/STABLE/VOLATILE designation,
or completely separate?

Regards,
	Jeff Davis