Re: A WalSnd issue related to state WALSNDSTATE_STOPPING

On Thu, Nov 22, 2018 at 1:29 PM Michael Paquier <michael(at)paquier(dot)xyz> wrote:

> On Wed, Nov 21, 2018 at 04:09:41PM +0900, Michael Paquier wrote:
> > The checkpointer initializes a shutdown checkpoint where it tells to all
> > the WAL senders to stop once all the children processes are gone, so it
> > seems to me that there is little point in processing
> > SyncRepReleaseWaiters() when a WAL sender is in WALSNDSTATE_STOPPING
> > state as at this stage syncrep makes little sense. It is still
> > necessary to process standby messages at this stage so as the primary
> > can shut down when it is sure that all the standbys have flushed the
> > shutdown checkpoint record of the primary.
>
> Just refreshed my memory with c6c33343, which is actually at the origin
> of the issue, and my previous argument is flawed. If a WAL sender has
> reached WALSNDSTATE_STOPPING no regular backends are around but a WAL
> sender could always commit a transaction in parallel which may need to
> make sure that its record is flushed and sync'ed, and this needs to make
> sure that waiters are correctly released. So it is necessary to patch
> up SyncRepGetSyncStandbysPriority and SyncRepGetSyncStandbysQuorum as
> mentioned upthread, perhaps adding a comment when looking at
> MyWalSnd->state looks adapted. Paul, would you like to write a patch?
> --
> Michael
>

Yes, please see the attached patch.