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

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Masahiko Sawada <sawada.mshk@gmail.com>, "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, Peter Smith <smithpb2250@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>
Date: 2022-12-26T14:05:24Z
Lists: pgsql-hackers 
On Mon, Dec 26, 2022 at 6:59 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>


In the commit message, there is a statement like this

"However, if the leader apply worker times out while attempting to
send a message to the
parallel apply worker, it will switch to "partial serialize" mode -  in this
mode the leader serializes all remaining changes to a file and notifies the
parallel apply workers to read and apply them at the end of the transaction."

I think it is a good idea to serialize the change to the file in this
case to avoid deadlocks, but why does the parallel worker need to wait
till the transaction commits to reading the file?  I mean we can
switch the serialize state and make a parallel worker pull changes
from the file and if the parallel worker has caught up with the
changes then it can again change the state to "share memory" and now
the apply worker can again start sending through shared memory.

I think generally streaming transactions are large and it is possible
that the shared memory queue gets full because of a lot of changes for
a particular transaction but later when the load switches to the other
transactions then it would be quite common for the worker to catch up
with the changes then it better to again take advantage of using
memory.  Otherwise, in this case, we are just wasting resources
(worker/shared memory queue) but still writing in the file.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com

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.