Re: logical replication and PANIC during shutdown checkpoint in publisher

On 12/04/17 15:55, Fujii Masao wrote:
> Hi,
>
> When I shut down the publisher while I repeated creating and dropping
> the subscription in the subscriber, the publisher emitted the following
> PANIC error during shutdown checkpoint.
>
> PANIC: concurrent transaction log activity while database system is
> shutting down
>
> The cause of this problem is that walsender for logical replication can
> generate WAL records even during shutdown checkpoint.
>
> Firstly walsender keeps running until shutdown checkpoint finishes
> so that all the WAL including shutdown checkpoint record can be
> replicated to the standby. This was safe because previously walsender
> could not generate WAL records. However this assumption became
> invalid because of logical replication. That is, currenty walsender for
> logical replication can generate WAL records, for example, by executing
> CREATE_REPLICATION_SLOT command. This is an oversight in
> logical replication patch, I think.

Hmm, but CREATE_REPLICATION_SLOT should not generate WAL afaik. I agree
that the issue with walsender still exist (since we now allow normal SQL
to run there) but I think it's important to identify what exactly causes
the WAL activity in your case - if it's one of the replication commands
and not SQL then we'll need to backpatch any solution we come up with to
9.4, if it's not replication command, we only need to fix 10.

--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services