On Wed, Jul 9, 2014 at 10:16 PM, Alvaro Herrera
<alvherre@2ndquadrant.com> wrote:
> there is no hardcoded assumption on the number of index
> values stored per heap column, so it is possible to build an opclass
> that stores a bounding box column for a geometry heap column, for
> instance.
I think the more Postgresy thing to do is to store one datum per heap
column. It's up to the opclass to find or make a composite data type
that stores all the necessary state. So you could make a minmax_accum
data type like NumericAggState in numeric.c:numeric_accum() or the
array of floats in float8_accum. For a bounding box a 2d geometric
min/max index could use the "box" data type for example. The way
you've done it seems more convenient but there's something to be said
for using the same style for different areas. A single bounding box
accumulator function would probably suffice for both an aggregate and
index opclass for example.
But this sounds pretty great. I think it would let me do the bloom
filter index I had in mind fairly straightforwardly. The result would
be something very similar to a bitmap index. I'm not sure if there's a
generic term that includes bitmap indexes or other summary functions
like bounding boxes (which min/max is basically -- a 1D bounding box).
Thanks a lot for listening and being so open, I think what you
describe is a lot more flexible than what you had before and I can see
some pretty great things coming out of it (including min/max itself of
course).
--
greg