Re: logical replication and PANIC during shutdown checkpoint in publisher

On 4/17/17 12:30, Andres Freund wrote:
>>>> So I guess that CREATE_REPLICATION_SLOT code calls LogStandbySnapshot()
>>>> and which generates WAL record about snapshot of running transactions.
>>>
>>> Erroring out in these cases sounds easy enough. Wonder if there's not a
>>> bigger problem with WAL records generated e.g. by HOT pruning or such,
>>> during decoding. Not super likely, but would probably hit exactly the
>>> same, no?
>>
>> Sounds possible, yes. Sounds like that's going to be nontrivial to fix
>> though.
>>
>> Another problem is that queries can run on walsender now. But that
>> should be possible to detect and shutdown just like backend.
>
> This sounds like a case for s/PANIC/ERROR|FATAL/ to me...

I'd imagine the postmaster would tell the walsender that it has started
shutdown, and then the walsender would reject $certain_things. But I
don't see an existing way for the walsender to know that shutdown has
been initiated. SIGINT is still free ...

The alternative of shutting down logical walsenders earlier also doesn't
look straightforward, since the postmaster doesn't know directly what
kind of walsender a certain process is. So you'd also need additional
signal types or something there.

--
Peter Eisentraut http://www.2ndQuadrant.com/
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