Horton

Re: row filtering for logical replication

Peter Smith <smithpb2250@gmail.com>

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From: Peter Smith <smithpb2250@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, Ajin Cherian <itsajin@gmail.com>, Greg Nancarrow <gregn4422@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: 2021-11-18T05:32:18Z
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 Mon, Nov 15, 2021 at 9:31 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Wed, Nov 10, 2021 at 12:36 PM Peter Smith <smithpb2250@gmail.com> wrote:
> >
> > On Mon, Nov 8, 2021 at 5:53 PM houzj.fnst@fujitsu.com
> > <houzj.fnst@fujitsu.com> wrote:
> > >
> > > 3) v37-0005
> > >
> > > - no parse nodes of any kind other than Var, OpExpr, Const, BoolExpr, FuncExpr
> > >
> > > I think there could be other node type which can also be considered as simple
> > > expression, for exmaple T_NullIfExpr.
> >
> > The current walker restrictions are from a previously agreed decision
> > by Amit/Tomas [1] and from an earlier suggestion from Andres [2] to
> > keep everything very simple for a first version.
> >
> > Yes, you are right, there might be some additional node types that
> > might be fine, but at this time I don't want to add anything different
> > without getting their approval to do so. Anyway, additions like this
> > are all candidates for a future version of this row-filter feature.
> >
>
> I think we can consider T_NullIfExpr unless you see any problem with the same.

Added in v40 [1]

> Few comments on the latest set of patches (v39*)
> =======================================
...
> 0003*
> 3. In pgoutput_row_filter(), the patch is finding pub_relid when it
> should already be there in RelationSyncEntry->publish_as_relid found
> during get_rel_sync_entry call. Is there a reason to do this work
> again?

Fixed in v40 [1]

>
> 4. I think we should add some comments in pgoutput_row_filter() as to
> why we are caching the row_filter here instead of
> get_rel_sync_entry()? That has been discussed multiple times so it is
> better to capture that in comments.

Added comment in v40 [1]

>
> 5. Why do you need a separate variable rowfilter_valid to indicate
> whether a valid row filter exists? Why exprstate is not sufficient?
> Can you update comments to indicate why we need this variable
> separately?

I have improved the (existing) comment in v40 [1].

>
> 0004*
> 6. In rowfilter_expr_checker(), the expression tree is traversed
> twice, can't we traverse it once to detect all non-allowed stuff? It
> can be sometimes costly to traverse the tree multiple times especially
> when the expression is complex and it doesn't seem acceptable to do so
> unless there is some genuine reason for the same.

I kind of doubt there would be any perceptible difference for 2
traverses instead of 1 because:
a) filters are limited to simple expressions. Yes, a large boolean
expression is possible but I don't think it is likely.
b) the validation part is mostly a one-time execution only when the
filter is created or changed.

Anyway, I am happy to try to refactor the logic to a single traversal
as suggested, but I'd like to combine those "validation" patches
(v40-0005, v40-0006) first, so I can combine their walker logic. Is it
OK?

>
> 7.
> +static void
> +rowfilter_expr_checker(Publication *pub, Node *rfnode, Relation rel)
>
> Keep the rel argument before whereclause as that makes the function
> signature better.

Fixed in v40 [1]

-----
[1] https://www.postgresql.org/message-id/CAHut%2BPv-D4rQseRO_OzfEz2dQsTKEnKjBCET9Z-iJppyT1XNMQ%40mail.gmail.com

Kind Regards,
Peter Smith.
Fujitsu Australia