Re: allow online change primary_conninfo

Hello

Updated patch attached. (also I merged into one file)

> + <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).

Changed.

> 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.

Changed to "Process any requests or signals received recently." like in other places, e.g. syslogger

> 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.

I renamed to pendingWalRcvRestart and replaced switch with simple condition.

> 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.

As I answered earlier, here is no switch to archive or wal_retrieve_retry_interval waiting in my patch. I recheck on current revision too:

2019-08-28 12:16:27.295 MSK 11180 @ from  [vxid: txid:0] [] DEBUG:  sending write 0/30346C8 flush 0/30346C8 apply 0/30346C8
2019-08-28 12:16:27.493 MSK 11172 @ from  [vxid: txid:0] [] LOG:  received SIGHUP, reloading configuration files
2019-08-28 12:16:27.494 MSK 11172 @ from  [vxid: txid:0] [] LOG:  parameter "primary_conninfo" changed to "host='/tmp' port=5555 sslmode=disable sslcompression=0 gssencmode=disable target_session_attrs=any"
2019-08-28 12:16:27.496 MSK 11173 @ from  [vxid:1/0 txid:0] [] LOG:  The WAL receiver is going to be restarted due to change of primary_conninfo
2019-08-28 12:16:27.496 MSK 11176 @ from  [vxid: txid:0] [] DEBUG:  checkpointer updated shared memory configuration values
2019-08-28 12:16:27.496 MSK 11180 @ from  [vxid: txid:0] [] FATAL:  terminating walreceiver process due to administrator command
2019-08-28 12:16:27.500 MSK 11335 @ from  [vxid: txid:0] [] LOG:  started streaming WAL from primary at 0/3000000 on timeline 1
2019-08-28 12:16:27.500 MSK 11335 @ from  [vxid: txid:0] [] DEBUG:  sendtime 2019-08-28 12:16:27.50037+03 receipttime 2019-08-28 12:16:27.500821+03 replication apply delay 0 ms transfer latency 0 ms

No "DEBUG:  switched WAL source from stream to archive after failure" messages, no time difference (wal_retrieve_retry_interval = 5s).

regards, Sergei