Marko A. Rodriguez created TINKERPOP-1254:
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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?
{code}
g.V.as('a').out().as('b').out().where(neq('a').and().neq('b')).both().name
{code}
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:
{code}
traverser.dropLabels(Set<String>)
traverser.dropPath()
{code}
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:
{code}
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);
}
}
{code}
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()}}.
{code}
g.V().match(
a.out.b,
b.out.c,
c.neq.a,
c.out.b,
).select("a")
{code}
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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