Minor Description
Currently the function processNextStart , hasNextBarrier, nextBarrier of AggregateStep all call AggregateStep.processAllStarts:
protected Traverser.Admin<S> processNextStart() {
this.processAllStarts();
return this.barrier.remove();
}
Every time we get a traverser from AggregateStep, AggregateStep.processAllStarts will be called. Then processAllStarts calls this.starts.hasNext().
@Override
public void processAllStarts() {
if (this.starts.hasNext()) {
final BulkSet<Object> bulkSet = new BulkSet<>();
while (this.starts.hasNext()) {
final Traverser.Admin<S> traverser = this.starts.next();
bulkSet.add(TraversalUtil.applyNullable(traverser, this.aggregateTraversal), traverser.bulk());
traverser.setStepId(this.getNextStep().getId()); // when barrier is reloaded, the traversers should be at the next step
this.barrier.add(traverser);
}
this.getTraversal().getSideEffects().add(this.sideEffectKey, bulkSet);
}
}
It results in a lot of hasNext call.
As document says "The step uses eager evaluation in that no objects continue on until all previous objects have been fully aggregated." maybe we can limit the AggregateStep.processAllStarts only be called once.
We found this when we run DSL like this :
g.V().has('name','wxy').repeat(both("knows").simplePath()).emit().times(2).aggregate("friends")
and the plan is like this :
GraphStep(vertex,[name.eq(wxy)]), RepeatStep([VertexStep(BOTH,[knows],vertex), PathFilterStep(simple), RepeatEndStep],until(loops(2)),emit(true)), AggregateStep(friends)
Then we found thousands of calls to GraphStep(vertex,[name.eq(wxy)]).hasNext.
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