[postgis-users] Strange result about spatial indexes?

[Paul Ramsey]

My guess is that it will manifest only with tables of large objects,
particularly if they break the toast barrier. I am still waiting for a
sample data set I can download, that link didn't work for me at all.

P.

On Fri, Aug 14, 2009 at 9:15 AM, Kevin Neufeld<kneufeld at refractions.net> wrote:
> Paragon Corporation wrote:
>>
>> Kevin et al,
>>
>> Interesting.  What is there to discover? That you can force choice of
>> index?
>>
>
> No, not that you can force the planner.  You'll notice in my 3 examples, the
> first and the last queries have the exact same plan, but the 3rd runs in
> half the time.
>
> What's interesting here is that postgresql is caching expand() calls
> differently than a simple &&, improving I/O performance significantly.
>
> [time passes]
> Ok, so, I just did a bunch more testing on 8.2 and 8.3 and it turns out that
> I can't reproduce the results on any of the newer postgis installs (1.4.0,
> 1.4.1SVN).  The version I was using to yield the strange caching behaviour
> was (shamefully) 1.1 running on 8.2.
>
> So I withdrawn my previous "discover" comments :)
>
> -- Kevin
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