Re: 2-phase commit

> Not "it can", but "it has to".  The master *must* keep hold of that
> request forever (or until the slave responds, or until we reconfigure
> the system not to consider that slave valid anymore).  Similarly, the
> slave cannot forget the maybe-committed transaction on pain of not being
> a valid slave anymore.  You can make this work, but the resource costs
> are steep.  For instance, in Postgres, you don't get to truncate the WAL
> log, for what could be a really really long time --- more disk space
> than you wanted to spend on WAL anyway.  The locks held by the
> maybe-committed transaction are another potentially unpleasant problem;
> you can't release them, no matter what else they are blocking.

So, after 'n' seconds of waiting, we abandon the slave and the slave
abandons the master.

Such a condition is probably a fairly serious failure anyway, and
something that an admin would need to expect.  The admin would also need
to expect to allocate a heap of disk space for WAL.

Chris