Re: Bad optimizer data for xml (WAS: xml data type implications of no =)

Mark Kirkwood <mark.kirkwood@catalyst.net.nz> writes:
> It seems that the nub of this issue is that there are conceptually two
> types of =, one for datatype specific comparison, and one for optimizer
> statistical information calculation. However the system allows only the
> first, so if you don't (or can't) have one then you lose some possibly
> important optimization data.

Nonsense.  ANALYZE and the optimizer work with the datatype's usual
notion of '=', whatever it is.

It's possible that we should install a simplified code path in analyze.c
that can collect width data for a column even in the absence of any '='
operator.  I'm less than convinced that it's worth the trouble though.
Do you have an actual example where such data would have affected a
plan choice?

            regards, tom lane