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Re: Perform streaming logical transactions by background workers and parallel apply

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Peter Smith <smithpb2250@gmail.com>
Cc: "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-07-01T09:43:34Z
Lists: pgsql-hackers 
On Fri, Jul 1, 2022 at 12:13 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> ======
>
> 1.2 doc/src/sgml/protocol.sgml - Protocol constants
>
> Previously I wrote that since there are protocol changes here,
> shouldn’t there also be some corresponding LOGICALREP_PROTO_XXX
> constants and special checking added in the worker.c?
>
> But you said [1 comment #6] you think it is OK because...
>
> IMO, I still disagree with the reply. The fact is that the protocol
> *has* been changed, so IIUC that is precisely the reason for having
> those protocol constants.
>
> e.g I am guessing you might assign the new one somewhere here:
> --
>     server_version = walrcv_server_version(LogRepWorkerWalRcvConn);
>     options.proto.logical.proto_version =
>         server_version >= 150000 ? LOGICALREP_PROTO_TWOPHASE_VERSION_NUM :
>         server_version >= 140000 ? LOGICALREP_PROTO_STREAM_VERSION_NUM :
>         LOGICALREP_PROTO_VERSION_NUM;
> --
>
> And then later you would refer to this new protocol version (instead
> of the server version) when calling to the apply_handle_stream_abort
> function.
>
> ======
>

One point related to this that occurred to me is how it will behave if
the publisher is of version >=16 whereas the subscriber is of versions
<=15? Won't in that case publisher sends the new fields but
subscribers won't be reading those which may cause some problems.

> ======
>
> 1.5 src/backend/commands/subscriptioncmds.c
>
> + /*
> + * If no parameter given, assume "true" is meant.
> + */
>
> Previously I suggested an update for this comment, but it was rejected
> [1 comment #12] saying you wanted consistency with defGetBoolean.
>
> Sure, that is one point of view. Another one is that "two wrongs don't
> make a right". IIUC that comment as it currently stands is incorrect
> because in this case there *is* a parameter given - it is just the
> parameter *value* that is missing.
>

You have a point but if we see this function in the vicinity then the
proposed comment also makes sense.

-- 
With Regards,
Amit Kapila.

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Fix invalid memory access during the shutdown of the parallel apply worker.

  2. Fix assertion failure in apply worker.

  3. Use elog to report unexpected action in handle_streamed_transaction().

  4. Use appropriate wait event when sending data in the apply worker.

  5. Allow the logical_replication_mode to be used on the subscriber.

  6. Rename GUC logical_decoding_mode to logical_replication_mode.

  7. Display the leader apply worker's PID for parallel apply workers.

  8. Improve the code to decide and process the apply action.

  9. Document the newly added wait events added by commit 216a784829.

  10. Perform apply of large transactions by parallel workers.

  11. Wake up a subscription's replication worker processes after DDL.

  12. Add copyright notices to meson files

  13. Better document logical replication parameters

  14. Add a common function to generate the origin name.

  15. Harmonize parameter names in storage and AM code.

  16. Avoid using list_length() to test for empty list.

  17. Improve two comments related to a boolean DefElem's value

  18. Fix partition table's REPLICA IDENTITY checking on the subscriber.

  19. Fix data inconsistency between publisher and subscriber.

  20. Fix cache look-up failures while applying changes in logical replication.