Re: allow online change primary_conninfo

On Mon, Jul 01, 2019 at 02:33:39PM +0300, Sergei Kornilov wrote:
> Updated version attached. Merge conflict was about tests count in
> 001_stream_rep.pl. Nothing else was changed. My approach can be
> still incorrect, any redesign ideas are welcome. Thanks in advance!

It has been some time, and I am finally catching up with this patch.

+ <para>
+ WAL receiver will be restarted after <varname>primary_slot_name</varname>
+ was changed.
</para>
The sentence sounds strange. Here is a suggestion:
The WAL receiver is restarted after an update of primary_slot_name (or
primary_conninfo).

The comment at the top of the call of ProcessStartupSigHup() in
HandleStartupProcInterrupts() needs to be updated as it mentions a
configuration file re-read, but that's not the case anymore.

pendingRestartSource's name does not represent what it does, as it is
only associated with the restart of a WAL receiver when in streaming
state, and that's a no-op for the archive mode and the local mode.

So, the patch splits the steps taken when checking for a WAL source by
adding an extra step after the failure handling that you are calling
the restart step. When a failure happens for the stream mode
(shutdown of WAL receiver, promotion. etc), there is a switch to the
archive mode, and nothing is changed in this case in your patch. So
when shutting down the WAL receiver after a parameter change, what
happens is that the startup process waits for retrieve_retry_interval
before moving back to the archive mode. Only after scanning again the
archives do we restart a new WAL receiver. However, if the restart of
the WAL receiver is planned because of an update of primary_conninfo
(or slot), shouldn't the follow-up mode be XLOG_FROM_STREAM without
waiting for wal_retrieve_retry_interval ms for extra WAL to become
available?
--
Michael