[postgis-devel] Caching Double-based Boxes

[Mark Cave-Ayland]

On 29/11/11 14:14, Paul Ramsey wrote:

> Well, two things (and notice to reader, we're discussing the doublebox
> spike here):
> - on the side of expected slowdown (systematic problem), we're pushing
> twice as much data through the pipes (reading cached double instead of
> cached float) to get the answer we want

True, but I'd expect this effect to be minimal or perhaps a couple of 
percent at most.

> - on the side of the unexpected slowdown (operator problem (Paul
> error)), in order to do the comparisons between the cache keys
> (doubles) and the index keys (floats) the cache keys now all have to
> be converted to floats before the comparison so there's an extra step
> in there that doesn't exist in the pure-float (cached float and float
> indexes) implementation

Now this might go some way to explaining some of it, although again most 
of this is speculation without a profile.


ATB,

Mark.

-- 
Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
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