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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: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, shveta malik <shveta.malik@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>, Peter Smith <smithpb2250@gmail.com>
Date: 2023-02-03T09:44:17Z
Lists: pgsql-hackers 
On Fri, Feb 3, 2023 at 1:28 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Fri, Feb 3, 2023 at 12:29 PM houzj.fnst@fujitsu.com
> <houzj.fnst@fujitsu.com> wrote:
> >
> > On Friday, February 3, 2023 11:04 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > >
> > > On Thu, Feb 2, 2023 at 4:52 AM Peter Smith <smithpb2250@gmail.com>
> > > wrote:
> > > >
> > > > Some minor review comments for v91-0001
> > > >
> > >
> > > Pushed this yesterday after addressing your comments!
> >
> > Thanks for pushing.
> >
> > Currently, we have two remaining patches which we are not sure whether it's worth
> > committing for now. Just share them here for reference.
> >
> > 0001:
> >
> > Based on our discussion[1] on -hackers, it's not clear that if it's necessary
> > to add the sub-feature to stop extra worker when
> > max_apply_workers_per_suibscription is reduced. Because:
> >
> > - it's not clear whether reducing the 'max_apply_workers_per_suibscription' is very
> >   common.
>
> A use case I'm concerned about is a temporarily intensive data load,
> for example, a data loading batch job in a maintenance window. In this
> case, the user might want to temporarily increase
> max_parallel_workers_per_subscription in order to avoid a large
> replication lag, and revert the change back to normal after the job.
> If it's unlikely to stream the changes in the regular workload as
> logical_decoding_work_mem is big enough to handle the regular
> transaction data, the excess parallel workers won't exit.
>

Won't in such a case, it would be better to just switch off the
parallel option for a subscription? We need to think of a predictable
way to test this path which may not be difficult. But I guess it would
be better to wait for some feedback from the field about this feature
before adding more to it and anyway it shouldn't be a big deal to add
this later as well.

-- 
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.