> 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