On Fri, Jun 14, 2013 at 12:20 PM, Heikki Linnakangas
<hlinnakangas@vmware.com> wrote:
> For pg_rewind, we wouldn't actually need a full-page image for hint bit
> updates, just a small record saying "hey, I touched this page". And you'd
> only need to write that the first time a page is touched after a checkpoint.
I would expect that to be about the same cost though. The latency for
the fsync on the wal record before being able to flush the buffer is
the biggest cost.
> The proposed patch is clearly not 9.3 material either. If anything, there's
> a much better change that we could still sneak in a GUC to allow hint bits
> to be WAL-logged without checksums in 9.3. All the code is there, it'd just
> be a new guc to control it separetely from checksums.
On the other hand if you're going to wal log the hint bits why not
enable checksums?
Do we allow turning off checksums after a database is initdb'd? IIRC
we can't turn it on later but I don't see why we couldn't turn them
off.
--
greg
