On 14/04/17 19:33, Fujii Masao wrote:
> On Fri, Apr 14, 2017 at 10:33 PM, Petr Jelinek
> <petr.jeli...@2ndquadrant.com> wrote:
>> 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
> At least in my case, the following CREATE_REPLICATION_SLOT command
> generated WAL record.
> Here is the pg_waldump output of the WAL record that CREATE_REPLICATION_SLOT
> generated.
>     rmgr: Standby     len (rec/tot):     24/    50, tx:          0,
> lsn: 0/01601438, prev 0/01601400, desc: RUNNING_XACTS nextXid 692
> latestCompletedXid 691 oldestRunningXid 692
> So I guess that CREATE_REPLICATION_SLOT code calls LogStandbySnapshot()
> and which generates WAL record about snapshot of running transactions.

Ah yes looking at the code, it does exactly that (on master only). Means
that backport will be necessary.

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

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