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 solesynchronous standby.  At any time there can be only one
synchronousstandbyserver.  The first standby to connect that is listed herewill become the synchronous standby server.
Otherstandby serversthat connect will then become potential synchronous standbys.If the current synchronous standby
disconnectsfor whatever reasonit will be replaced with one of the potential standbys.Specifying more than one standby
namecan allow very high availability.
 
The standby name is currently taken as the application_name of thestandby, as set in the primary_conninfo on the
standby.Names arenot enforced for uniqueness, though clearly that could lead toconfusion and misconfiguration.
Specifyingmultiple standbys with thesame name does not allow more than one standby to be the currentsynchronous
standby.
If a standby is removed from the list of servers then it will stopbeing the synchronous standby, allowing another to
takeit's place.Standbys may also be added to the list without restarting the server.
 

-- Simon Riggs           http://www.2ndQuadrant.com/books/PostgreSQL Development, 24x7 Support, Training and Services