On Thu, Jul 31, 2014 at 5:26 AM, desmodemone <desmodem...@gmail.com> wrote:
> b) yes the backends need to update the map, but it's in memory, and as I
> show, could be very small if we you chunk of blocks.If we not compress the
> map, I not think could be a bottleneck.

If it's in memory, it's not crash-safe. For something aimed at
backups, I think crash safety is a requirement. So it's at least one
extra I/O per commit, maybe less if many can be coalesced at
checkpoints, but I wouldn't count on it too much, because worst cases
are easy to come by (sparse enough updates).

I think this could be pegged on WAL replay / checkpoint stuff alone,
so it would be very asynchronous, but not free.

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