Actually the JTS Java library (which PostGIS uses the C port of) is
generally quite a bit faster than the same routine inside PostGIS. The
"maths" is not the hot spot in the geometric routines.
There are reasons why you might not want to load all data into
client-side memory (eg code complexity and data volume) but performance
is *not* one of them.
The best caching that you can do for this case is to use a
PreparedGeometry for your target "large data". PostGIS does some of
this already, although it may or may not be able to be applied in your
queries. If you implement this client-side in Java you can easily
construct your code so that all tests are carried out against
PreparedGeometrys.
Brian Modra wrote:
2009/11/24 tommy408 <[email protected]>:
I have a web application that requires a lot of queries, like 200 queries a
second. And they're mostly running ST_Within on large data. Should I just
load the data into memory to do the calculations ( I'm using java) or keep
them in postgres and run the queries? I don't know if database already
doing caching.
ST_within is a function, as far as I know, its not doing its own caching.
But the database does naturally cache. So if you do the same query
again, it won't have to do so much IO... and the gist index will
probably also be in cache.
You'll have to benchmark it yourself, because it depends a lot on your
data and query.
But caching and doing the calculations in memory using Java will
likely be slow anyway if the data is large, because Java is not great
for maths. Rather cache one complete result with its query data, and
then if a matching query comes in, you have the results already. But
let the database find the result in the first place rather than do the
maths in Java.
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Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
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