Re: Get stuck when dropping a subscription during synchronizing table

On Mon, May 08, 2017 at 06:27:30PM +0900, Masahiko Sawada wrote:
> I encountered a situation where DROP SUBSCRIPTION got stuck when
> initial table sync is in progress. In my environment, I created
> several tables with some data on publisher. I created subscription on
> subscriber and drop subscription immediately after that. It doesn't
> always happen but I often encountered it on my environment.
>
> ps -x command shows the following.
>
> 96796 ? Ss 0:00 postgres: masahiko postgres [local] DROP
> SUBSCRIPTION
> 96801 ? Ts 0:00 postgres: bgworker: logical replication
> worker for subscription 40993 waiting
> 96805 ? Ss 0:07 postgres: bgworker: logical replication
> worker for subscription 40993 sync 16418
> 96806 ? Ss 0:01 postgres: wal sender process masahiko [local] idle
> 96807 ? Ss 0:00 postgres: bgworker: logical replication
> worker for subscription 40993 sync 16421
> 96808 ? Ss 0:00 postgres: wal sender process masahiko [local] idle
>
> The DROP SUBSCRIPTION process (pid 96796) is waiting for the apply
> worker process (pid 96801) to stop while holding a lock on
> pg_subscription_rel. On the other hand the apply worker is waiting for
> acquiring a tuple lock on pg_subscription_rel needed for heap_update.
> Also table sync workers (pid 96805 and 96807) are waiting for the
> apply worker process to change their status.
>
> Also, even when DROP SUBSCRIPTION is done successfully, the table sync
> worker can be orphaned because I guess that the apply worker can exit
> before change status of table sync worker.
>
> I'm using 1f30295.

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The above-described topic is currently a PostgreSQL 10 open item. Peter,
since you committed the patch believed to have created it, you own this open
item. If some other commit is more relevant or if this does not belong as a
v10 open item, please let us know. Otherwise, please observe the policy on
open item ownership[1] and send a status update within three calendar days of
this message. Include a date for your subsequent status update. Testers may
discover new open items at any time, and I want to plan to get them all fixed
well in advance of shipping v10. Consequently, I will appreciate your efforts
toward speedy resolution. Thanks.

[1] https://www.postgresql.org/message-id/20170404140717.GA2675809%40tornado.leadboat.com