Re: logical replication and PANIC during shutdown checkpoint in publisher

On Thu, Apr 13, 2017 at 12:36 PM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> wrote:
> On Thu, Apr 13, 2017 at 12:28 PM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
>> On Thu, Apr 13, 2017 at 5:25 AM, Peter Eisentraut
>> <peter(dot)eisentraut(at)2ndquadrant(dot)com> wrote:
>>> On 4/12/17 09:55, Fujii Masao wrote:
>>>> To fix this issue, we should terminate walsender for logical replication
>>>> before shutdown checkpoint starts. Of course walsender for physical
>>>> replication still needs to keep running until shutdown checkpoint ends,
>>>> though.
>>>
>>> Can we turn it into a kind of read-only or no-new-commands mode instead,
>>> so it can keep streaming but not accept any new actions?
>>
>> So we make walsenders switch to that mode and wait for all the already-ongoing
>> their "write" commands to finish, and then we start a shutdown checkpoint?
>> This is an idea, but seems a bit complicated. ISTM that it's simpler to
>> terminate only walsenders for logical rep before shutdown checkpoint.
>
> Perhaps my memory is failing me here... But in clean shutdowns we do
> shut down WAL senders after the checkpoint has completed so as we are
> sure that they have flushed the LSN corresponding to the checkpoint
> ending, right?

Yes.

> Why introducing an inconsistency for logical workers?
> It seems to me that logical workers should fail under the same rules.

Could you tell me why? You think that even walsender for logical rep
needs to stream the shutdown checkpoint WAL record to the subscriber?
I was not thinking that's true.

Regards,

--
Fujii Masao