Horton

Re: Exit walsender before confirming remote flush in logical replication

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2022-12-28T03:56:29Z
Lists: pgsql-hackers

Commits

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

  1. Add wal_sender_shutdown_timeout GUC to limit shutdown wait for replication

  2. pg_upgrade: Add --copy option

  3. Prevent possibility of panics during shutdown checkpoint.

  4. Support clean switchover.

On Wed, Dec 28, 2022 at 8:19 AM Hayato Kuroda (Fujitsu)
<kuroda.hayato@fujitsu.com> wrote:
>
> > In logical replication, it can happen today as well without
> > time-delayed replication. Basically, say apply worker is waiting to
> > acquire some lock that is already acquired by some backend then it
> > will have the same behavior. I have not verified this, so you may want
> > to check it once.
>
> Right, I could reproduce the scenario with following steps.
>
> 1. Construct pub -> sub logical replication system with streaming = off.
> 2. Define a table on both nodes.
>
> ```
> CREATE TABLE tbl (id int PRIMARY KEY);
> ```
>
> 3. Execute concurrent transactions.
>
> Tx-1 (on subscriber)
> BEGIN;
> INSERT INTO tbl SELECT i FROM generate_series(1, 5000) s(i);
>
>         Tx-2 (on publisher)
>         INSERT INTO tbl SELECT i FROM generate_series(1, 5000) s(i);
>
> 4. Try to shutdown publisher but it will be failed.
>
> ```
> $ pg_ctl stop -D publisher
> waiting for server to shut down............................................................... failed
> pg_ctl: server does not shut down
> ```

Thanks for the verification. BTW, do you think we should document this
either with time-delayed replication or otherwise unless this is
already documented?

Another thing we can investigate here why do we need to ensure that
there is no pending send before shutdown.

-- 
With Regards,
Amit Kapila.