[postgis-devel] Regression performance.

[Sandro Santilli]

On Thu, Feb 09, 2012 at 04:14:12PM -0800, David Zwarg wrote:

> A note on the surprising factor: it took myself and David Bronough at the
> code sprint all day to profile and identify what was happening. Both of us
> were looking at the patch from r9112, scratching our heads.  The removal of
> strstr should have made it faster, but it turns out the use of integers in
> the expressions were doing something in the parser/planner/evaluator for
> every pixel, and this was slowing everything down.  It doesn't make sense
> on many levels, and I would have thought that integer math would be faster
> that floating point math, but in this case it is not the case. Something in
> the way postgres evaluates that parameterized query changes that
> assumption, which I have no knowledge of (thus the mystery for me).

Did your expression include math on the [rast.x] and [rast.y] values ?

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