On Mon, Mar 18, 2013 at 5:52 PM, Bruce Momjian <bruce@momjian.us> wrote:
> With a potential 10-20% overhead, I am unclear who would enable this at
> initdb time.
For what it's worth I think cpu overhead of the checksum is totally a
red herring.. Of course there's no reason not to optimize it to be as
fast as possible but if we say there's a 10% cpu overhead due to
calculating the checksum users will think that's perfectly reasonable
trade-off and have no trouble looking at their cpu utilization and
deciding whether they have that overhead to spare. They can always buy
machines with more cores anyways.
Added I/O overhead, especially fsync latency is the performance impact
that I think we should be focusing on. Uses will be totally taken by
surprise to hear that checksums require I/O. And fsync latency to the
xlog is very very difficult to reduce. You can buy more hard drives
until the cows come home and the fsync latency will hardly change.
--
greg