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From "Marko A. Rodriguez (JIRA)" <j...@apache.org>
Subject [jira] [Created] (TINKERPOP-1254) Support dropping traverser path information when it is no longer needed.
Date Thu, 07 Apr 2016 18:14:25 GMT
Marko A. Rodriguez created TINKERPOP-1254:

             Summary: Support dropping traverser path information when it is no longer needed.
                 Key: TINKERPOP-1254
                 URL: https://issues.apache.org/jira/browse/TINKERPOP-1254
             Project: TinkerPop
          Issue Type: Improvement
          Components: process
    Affects Versions: 3.1.1-incubating
            Reporter: Marko A. Rodriguez

The most expensive traversals (especially in OLAP) are those that can not be "bulked." There
are various reasons why two traversers at the same object can not be bulked, but the primary
reason is {{PATH}} or {{LABELED_PATH}}. That is, when the history of the traverser is required,
the probability of two traversers having the same history is low.

A key to making traversals more efficient is to do as a much as possible to remove historic
information from a traverser so it can get bulked. How does one do this? 


The {{LABELED_PATH}} of "a" and "b" are required up to the {{where()}} and at which point,
at {{both()}}, they are no longer required. It would be smart to support:


We would then, via a {{TraversalOptimizationStrategy}} insert a step between {{where()}} and
{{both()}} called {{PathPruneStep}} which would be a {{SideEffectStep}}. The strategy would
know which labels were no longer needed (via forward lookahead) and then do:

public class PathPruneStep {
  final Set<String> dropLabels = ...
  final boolean dropPath = ...

  public void sideEffect(final Traverser<S> traverser) {
    final Traverser<S> start = this.starts.next();
    if(this.dropPath) start.dropPath();
    else start.dropLabels(labels); 

Again, the more we can prune historic path data no longer needed, the higher the probability
of bulking. Think about this in terms of {{match()}}.


All we need is "a" at the end. Thus, once a pattern has been passed and no future patterns
require that label, drop it! 

This idea is related to TINKERPOP-331, but I don't think we should deal with manipulating
the species. Thus, I think 331 is too "low level."

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