On 10/31/2017 01:47 PM, Jody Garnett wrote:
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]
<mailto:[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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