Re: logical replication and PANIC during shutdown checkpoint in publisher

On 4/21/17 00:11, Michael Paquier wrote:
> Hmm. I have been actually looking at this solution and I am having
> doubts regarding its robustness. In short this would need to be
> roughly a two-step process:
> - In PostmasterStateMachine(), SIGUSR2 is sent to the checkpoint to
> make it call ShutdownXLOG(). Prior doing that, a first signal should
> be sent to all the WAL senders with
> SignalSomeChildren(BACKEND_TYPE_WALSND). SIGUSR2 or SIGINT could be
> used.
> - At reception of this signal, all WAL senders switch to a stopping
> state, refusing commands that can generate WAL.
> - Checkpointer looks at the state of all WAL senders, looping with a
> sleep call of a couple of ms, refusing to launch the shutdown
> checkpoint as long as all WAL senders have not switched to the
> stopping state.
> - In reaper(), once checkpointer is confirmed as stopped, signal again
> the WAL senders, and tell them to perform the last loop.

Yeah that looks like a reasonable approach.

I'm not sure why in your patch you process got_SIGUSR2 in
WalSndErrorCleanup() instead of in the main loop.

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