Horton

Re: row filtering for logical replication

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Peter Smith <smithpb2250@gmail.com>, "tanghy.fnst@fujitsu.com" <tanghy.fnst@fujitsu.com>, Euler Taveira <euler@eulerto.com>, Greg Nancarrow <gregn4422@gmail.com>, vignesh C <vignesh21@gmail.com>, Ajin Cherian <itsajin@gmail.com>, Dilip Kumar <dilipbalaut@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>, Amit Langote <amitlangote09@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-01-20T13:13:35Z
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

I was skimming this and the changes in CheckCmdReplicaIdentity caught my
attention.  "Is this code running at the publisher side or the subscriber
side?" I wondered -- because the new error messages being added look
intended to be thrown at the publisher side; but the existing error
messages appear intended for the subscriber side.  Apparently there is
one caller at the publisher side (CheckValidResultRel) and three callers
at the subscriber side.  I'm not fully convinced that this is a problem,
but I think it's not great to have it that way.  Maybe it's okay with
the current coding, but after this patch adds this new errors it is
definitely weird.  Maybe it should split in two routines, and document
more explicitly which is one is for which side.

And while wondering about that, I stumbled upon
GetRelationPublicationActions(), which has a very weird API that it
always returns a palloc'ed block -- but without saying so.  And
therefore, its only caller leaks that memory.  Maybe not critical, but
it looks ugly.  I mean, if we're always going to do a memcpy, why not
use a caller-supplied stack-allocated memory?  Sounds like it'd be
simpler.

And the actual reason I was looking at this code, is that I had stumbled
upon the new GetRelationPublicationInfo() function, which has an even
weirder API:

>  * Get the publication information for the given relation.
>  *
>  * Traverse all the publications which the relation is in to get the
>  * publication actions and validate the row filter expressions for such
>  * publications if any. We consider the row filter expression as invalid if it
>  * references any column which is not part of REPLICA IDENTITY.
>  *
>  * To avoid fetching the publication information, we cache the publication
>  * actions and row filter validation information.
>  *
>  * Returns the column number of an invalid column referenced in a row filter
>  * expression if any, InvalidAttrNumber otherwise.
>  */
> AttrNumber
> GetRelationPublicationInfo(Relation relation, bool validate_rowfilter)

"Returns *an* invalid column referenced in a RF if any"?  That sounds
very strange.  And exactly what info is it getting, given that there is
no actual returned info?  Maybe this was meant to be "validate RF
expressions" and return, perhaps, a bitmapset of all invalid columns
referenced?  (What is an invalid column in the first place?)


In many function comments you see things like "Check, if foo is bar" or
"Returns true, if blah".  These commas there needs to be removed.

Thanks

-- 
Álvaro Herrera           39°49'30"S 73°17'W  —  https://www.EnterpriseDB.com/
"I dream about dreams about dreams", sang the nightingale
under the pale moon (Sandman)