Horton

Re: row filtering for logical replication

Greg Nancarrow <gregn4422@gmail.com>

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From: Greg Nancarrow <gregn4422@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Euler Taveira <euler@eulerto.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: 2021-07-20T06:08:01Z
Lists: pgsql-hackers

Commits

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  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, Jul 20, 2021 at 2:25 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> Today, while studying the behavior of this particular operation in
> other databases, I found that IBM's InfoSphere Data Replication does
> exactly this. See [1]. I think there is a merit if want to follow this
> idea.
>

So in this model (after initial sync of rows according to the filter),
for UPDATE, the OLD row is checked against the WHERE clause, to know
if the row had been previously published. If it hadn't, and the NEW
row satisfies the WHERE clause, then it needs to be published as an
INSERT. If it had been previously published, but the NEW row doesn't
satisfy the WHERE condition, then it needs to be published as a
DELETE. Otherwise, if both OLD and NEW rows satisfy the WHERE clause,
it needs to be published as an UPDATE.
At least, that seems to be the model when the WHERE clause refers to
the NEW (updated) values, as used in most of their samples (i.e. in
that database "the current log record", indicated by a ":" prefix on
the column name).
I think that allowing the OLD values ("old log record") to be
referenced in the WHERE clause, as that model does, could be
potentially confusing.

Regards,
Greg Nancarrow
Fujitsu Australia