[postgis-devel] 1.3.3

[Mark Cave-Ayland]

On Friday 28 March 2008 23:53:53 Ben Jubb wrote:
> Howdy,
> In my testing, I did see a performance hit when using the memcmp test,
> although it was noticable only in the largest of my test geometries
> (5000 vertices or so).
> The three parameter form seemed like the best way to go because the
> whole point of the prepared version of the functions was to get the best
> possible performance.  The cases when the performance matters most is
> with large geoms, and then the cost of doing the memcmp is the highest.
> Using a third argument seemed the simplest way to get the best possible
> performance from the predicates, with a minimal increase in the
> complexity of the interface.
> I agree it would be nice to have a single form for those predicates that
> automatically determines the most efficient manner to do the tests, but
> there didn't seem to be any efficient way to accomplish that.
>
> b


Hi Ben,

Well I think it really comes down to what exactly is the performance hit and 
how did you measure it? Which platform/OS/C library did you use? Obviously 
there will be *some* overhead having the extra memcmp() in there but does it 
matter? For example, if the overhead is just 1-2s on a 30s query then that 
doesn't really matter. Then again, if the overhead is 1s on a 3s query then 
that is significant.

Since this is a new feature then I'd be inclined to say that for a first cut 
we should keep the standard API, and depending on the reports we get back, 
look at improving it later. That seems a lot more preferable to having a 
fairly nasty API hack that will catch a lot of people out :(


ATB,

Mark.

-- 
Mark Cave-Ayland
Sirius Corporation - The Open Source Experts
http://www.siriusit.co.uk
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