Re: [HACKERS] logical replication and PANIC during shutdowncheckpoint in publisher

On 20/04/17 05:57, Michael Paquier wrote:
> On Thu, Apr 20, 2017 at 12:40 PM, Michael Paquier
> <michael.paquier@gmail.com> wrote:
>> On Thu, Apr 20, 2017 at 4:57 AM, Peter Eisentraut
>> <peter.eisentraut@2ndquadrant.com> wrote:
>>> I think the problem with a signal-based solution is that there is no
>>> feedback.  Ideally, you would wait for all walsenders to acknowledge the
>>> receipt of SIGUSR2 (or similar) and only then proceed with the shutdown
>>> checkpoint.
>>
>> Are you sure that it is necessary to go to such extent? Why wouldn't
>> it be enough to prevent any replication commands generating WAL to run
>> when the WAL sender knows that the postmaster is in shutdown mode?
> 
> 2nd thoughts here... Ah now I see your point. True that there is no
> way to ensure that an unwanted command is not running when SIGUSR2 is
> received as the shutdown checkpoint may have already begun. Here is an
> idea: add a new state in WalSndState, say WALSNDSTATE_STOPPING, and
> the shutdown checkpoint does not run as long as all WAL senders still
> running do not reach such a state.
> 

+1 to this solution

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