Diff aggregations (deltas) about heroic HOT 5 CLOSED

Hey,

You are on the right track conceptually, but FilteringAggregation is not a great base for what you are trying to accomplish. I'd suggest investigating implementing a completely custom aggregation which wraps around Empty/EmptyInstance, and performs the delta's in the result method.

I realize this is what filtering aggregations do, but they are a bit more opinionated right now. What you do could be generalized into another aggregation archetype, maybe one that filtering should inherit from.

Good luck, and don't hesitate to follow up if you have more questions.

from heroic.

@udoprog Thanks, I'll keep you posted w/ progress & questions.

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@udoprog I've created Delta / DeltaInstance classes that extend Empty / EmptyInstance. It seems that CollectorSession in EmptyInstance is a private static final class. I'm not sure how to override the result function of a private class from within an extending class. Apologies, I am not a Java developer =( Would you be so kind as to set up the next few lines?

public class DeltaInstance extends EmptyInstance { @JsonCreator public DeltaInstance() { super(); } }

from heroic.

There´s no need to extend EmptyInstance, you can keep it as a field of DeltaInstance.

public class DeltaInstance {
    private final EmptyInstance inner = Empty.INSTANCE;

    /* implement methods and delegate calls to inner */
}

This is basically how it's used in FilteringAggregation here:
https://github.com/spotify/heroic/blob/master/aggregation/simple/src/main/java/com/spotify/heroic/aggregation/simple/FilterAggregation.java#L82

from heroic.

I've got a working Delta aggregation and will open a pull request later today for further discussion.

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