Greg Stark writes:
thousands of columns in which they have all but a handful be null.
They might be pretty happy about this.
On Tue, Apr 17, 2012 at 5:38 PM, Tom Lane 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 haveThis 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.
thousands of columns in which they have all but a handful be null.
They might be pretty happy about this.
dubious about how much we'd be slowing things down for everybody else.
As I said, what I'd like to see are some benchmarks, and not just
benchmarks that are tuned to match the sort of case where this wins.
regards, tom lane
