Re: 2-phase commit

On Fri, 26 Sep 2003, Tom Lane wrote:

> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > Could we allow slaves to check if the backend is still alive, perhaps by
> > asking the postmaster, similar to what we do with the cancel signal ---
> > that way, the slave would never time out and always wait if the master
> > was alive.
>
> You're not considering the possibility of a transient communication
> failure.  The fact that you cannot currently contact the other guy
> is not proof that he's not still alive.
>
> Example:
>
>     Master        Slave
>     ------        -----
>     commit ready-->
>             <--OK
>     commit done->XX
>
> where "->XX" means the message gets lost due to network failure.  Now

'k, but isn't alot of that a "retry" issue?  we're talking TCP here, not
UDP, which I *thought* was designed for transient network problems ... ?
I would think that any implementation would have a timeout/retry GUC
variable associated with it ... 'if no answer in x seconds, retry up to y
times' ...

if we are talking two computers sitting next to each other on a switch,
you'd expect those to be low ... but if you were talking about two
seperate geographical locations (and yes, I realize you are adding lag to
the mix with waiting for responses), you'd expect those #s to rise ...