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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: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, shveta malik <shveta.malik@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Dilip Kumar <dilipbalaut@gmail.com>
Date: 2023-01-13T03:36:55Z
Lists: pgsql-hackers 
On Fri, Jan 13, 2023 at 7:56 AM Peter Smith <smithpb2250@gmail.com> wrote:
>
> Here are my review comments for v79-0001.
>
> ======
>
> General
>
> 1.
>
> When Amit suggested [1] changing the name just to "leader_pid" instead
> of "leader_apply_pid" I thought he was only referring to changing the
> view column name, not also the internal member names of the worker
> structure. Maybe it is OK anyway, but please check if that was the
> intention.
>

Yes, that was the intention.

>
> 3.
>
>        <entry role="catalog_table_entry"><para role="column_definition">
> +       <structfield>leader_pid</structfield> <type>integer</type>
> +      </para>
> +      <para>
> +       Process ID of the leader apply worker if this process is a parallel
> +       apply worker; NULL if this process is a leader apply worker or does not
> +       participate in parallel apply, or a synchronization worker
> +      </para></entry>
>
> I felt this change is giving too many details and ended up just
> muddying the water.
>

I see that we give a similar description for other parameters as well.
For example leader_pid in pg_stat_activity, see client_dn,
client_serial in pg_stat_ssl. It is better to be consistent here and
this gives the reader a bit more information when the value is NULL
for the new column.

>
> 4.
>
> @@ -949,6 +949,7 @@ CREATE VIEW pg_stat_subscription AS
>              su.oid AS subid,
>              su.subname,
>              st.pid,
> +            st.leader_pid,
>              st.relid,
>              st.received_lsn,
>              st.last_msg_send_time,
>
> IMO it would be very useful to have an additional "kind" attribute for
> this view. This will save the user from needing to do mental
> gymnastics every time just to recognise what kind of process they are
> looking at.
>

This could be a separate enhancement as the same should be true for
sync workers.

-- 
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.