Re: Sync Rep v17

On Mon, 2011-02-21 at 21:35 +0900, Tatsuo Ishii wrote:
> > Well, good news all round.
> >
> > v17 implements what I believe to be the final set of features for sync
> > rep. This one I'm actually fairly happy with. It can be enjoyed best at
> > DEBUG3.
> >
> > The patch is very lite touch on a few areas of code, plus a chunk of
> > specific code, all on master-side. Pretty straight really. I'm sure
> > problems will be found, its not long since I completed this; thanks to
> > Daniel Farina for your help with patch assembly.
>
> + <primary><varname>synchronous_standby_names</> configuration parameter</primary>
> + </indexterm>
> + <listitem>
> + <para>
> + Specifies a list of standby names that can become the sole
> + synchronous standby. Other standby servers connect that are also on
> + the list become potential standbys. If the current synchronous standby
> + goes away it will be replaced with one of the potential standbys.
> + Specifying more than one standby name can allow very high availability.
> + </para>
>
> Can anybody please enlighten me? I do not quite follow "Other standby
> servers connect that are also on the list become potential standbys"
> part.
>
> Can I read this as "Other standby servers that are also on the list
> become potential synchrnous standbys"?

Yes

I have reworded it to see if that improves the explanation
Code available at git://github.com/simon2ndQuadrant/postgres.git

untagged text included here for clarity

synchronous_standby_names

Specifies a list of standby names that can become the sole
synchronous standby. At any time there can be only one synchronous
standby server. The first standby to connect that is listed here
will become the synchronous standby server. Other standby servers
that connect will then become potential synchronous standbys.
If the current synchronous standby disconnects for whatever reason
it will be replaced with one of the potential standbys.
Specifying more than one standby name can allow very high availability.

The standby name is currently taken as the application_name of the
standby, as set in the primary_conninfo on the standby. Names are
not enforced for uniqueness, though clearly that could lead to
confusion and misconfiguration. Specifying multiple standbys with the
same name does not allow more than one standby to be the current
synchronous standby.

If a standby is removed from the list of servers then it will stop
being the synchronous standby, allowing another to take it's place.
Standbys may also be added to the list without restarting the server.

--
Simon Riggs http://www.2ndQuadrant.com/books/
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