Opinion - great direction for visitor, think it would allow us to make
better use of collections model as a result. The functionality is used for
optimization in JDBC, but the ability to split/merge feature visitors
(including their result) would be advantageous for concurrency.
I remember exploring some of these design options when we looked at the
feature collection api; and there were examples from other languages being
considered.
Q: Now that we have a streaming API in Java does it offer any inspiration
or functionality that we could take advantage of?
--
Jody Garnett
On 31 October 2017 at 09:16, Andrea Aime <[email protected]>
wrote:
> Hi,
> I'm looking at a possible optimization for a composite feature collection,
> that is,
> the ability to optimize down feature visitors instead of running them in
> memory.
>
> So the code gets a visitor, and I was thinking, ok, if it's a FeatureCalc
> <https://github.com/geotools/geotools/blob/b0ddacc545aabeafc134cd0a050d0353829aca3b/modules/library/main/src/main/java/org/geotools/feature/visitor/FeatureCalc.java>
> there
> is
> a way to get the CalcResult(s) and merge them.
>
> However, the collection is given a FeatureCalc that might have aggregated
> something already in memory, that needs to be preserved, and at the end
> I need to set the "merge" result back into it.
>
> I looked into what JDBCDataStore can do, and it's basically using
> reflection
> to do its own business, since FeatureCalc per se provides no much methods.
>
> Thinking out loud maybe a "MutableFeatureCalc" is needed?
>
> interface MutableFeatureCalc extends FeatureCalc {
>
> // available in many implementations of FeatureCalc, but not all!
> public void reset();
>
> // this is what JDBCDataStore is relying upon
> public void setValue(Object result);
>
> }
>
> Then aggregating from N sources in a generic way would look something like:
>
> CalcResult result = calc.getResult();
> for(FeatureCollection fc : collections) {
> calc.reset();
> // need a wrapping sub progress listener here
> fc.accept(visitor, progressListener);
> CalcResult newResult = calc.getResult();
> result = result.merge(newResult);
> }
>
> calc.setValue(result.getValue());
>
>
> Opinions?
>
> Cheers
> Andrea
>
> PS: no promises it will be implemented, I'm in exploration and feasibility
> mode here
>
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