On Tue, Apr 17, 2012 at 5:38 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> This has been discussed before, but it always seemed that the
> cost-benefit ratio was exceedingly questionable. You don't get any
> savings whatsoever unless you reduce the size of the null bitmap across
> a MAXALIGN boundary, which more and more often is 64 bits, so that the
> frequency with which the optimization wins anything doesn't look likely
> to be that high.
There is the usage pattern where (brace yourself) people have
thousands of columns in which they have all but a handful be null.
They might be pretty happy about this. I'm not sure if that's a use
case that makes sense to optimize for though -- even for them the
space overhead would be noticeable but not a showstopper.
--
greg