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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>, "wangw.fnst@fujitsu.com" <wangw.fnst@fujitsu.com>, Peter Smith <smithpb2250@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, "shiy.fnst@fujitsu.com" <shiy.fnst@fujitsu.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-11-07T03:58:46Z
Lists: pgsql-hackers 
On Mon, Nov 7, 2022 at 8:26 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Sun, Nov 6, 2022 at 3:40 PM houzj.fnst@fujitsu.com
> <houzj.fnst@fujitsu.com> wrote:
> >
> > On Saturday, November 5, 2022 1:43 PM Amit Kapila <amit.kapila16@gmail.com>
> > >
> > > On Fri, Nov 4, 2022 at 7:35 PM houzj.fnst@fujitsu.com
> > > <houzj.fnst@fujitsu.com> wrote:
> > > >
> > > > On Friday, November 4, 2022 4:07 PM Amit Kapila
> > > <amit.kapila16@gmail.com> wrote:
> > > > >
> > > > > On Thu, Nov 3, 2022 at 6:36 PM houzj.fnst@fujitsu.com
> > > > > <houzj.fnst@fujitsu.com> wrote:
> > > > > >
> > > > > > Thanks for the analysis and summary !
> > > > > >
> > > > > > I tried to implement the above idea and here is the patch set.
> > > > > >
> > > > >
> > > > > Few comments on v42-0001
> > > > > ===========================
> > > >
> > > > Thanks for the comments.
> > > >
> > > > >
> > > > > 10.
> > > > > + winfo->shared->stream_lock_id = parallel_apply_get_unique_id();
> > > > > + winfo->shared->transaction_lock_id =
> > > > > + winfo->shared->parallel_apply_get_unique_id();
> > > > >
> > > > > Why can't we use xid (remote_xid) for one of these and local_xid
> > > > > (one generated by parallel apply) for the other?
> > > ...
> > > ...
> > > >
> > > > I also considered using xid for these locks, but it seems the objsubid
> > > > for the shared object lock is 16bit while xid is 32 bit. So, I tried
> > > > to generate a unique 16bit id here.
> > > >
> > >
> > > Okay, I see your point. Can we think of having a new lock tag for this with classid,
> > > objid, objsubid for the first three fields of locktag field? We can use a new
> > > macro SET_LOCKTAG_APPLY_TRANSACTION and a common function to set the
> > > tag and acquire the lock. One more point related to this is that I am suggesting
> > > classid by referring to SET_LOCKTAG_OBJECT as that is used in the current
> > > patch but do you think we need it for our purpose, won't subscription id and
> > > xid can uniquely identify the tag?
> >
> > I agree that it could be better to have a new lock tag. Another point is that
> > the remote xid and Local xid could be the same in some rare cases, so I think
> > we might need to add another identifier to make it unique.
> >
> > Maybe :
> > locktag_field1 : subscription oid
> > locktag_field2 : xid(remote or local)
> > locktag_field3 : 0(lock for stream block)/1(lock for transaction)
>
> Or I think we can use locktag_field2 for remote xid and locktag_field3
> for local xid.
>

We can do that way as well but OTOH, I think for the local
transactions we don't need subscription oid, so field1 could be
InvalidOid and field2 will be xid of local xact. Won't that be better?

-- 
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.