Daniel Kuppitz created TINKERPOP-1925:
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Summary: Don't apply PathRetractionStrategy recursively
Key: TINKERPOP-1925
URL: https://issues.apache.org/jira/browse/TINKERPOP-1925
Project: TinkerPop
Issue Type: Improvement
Components: process
Affects Versions: 3.2.7
Reporter: Daniel Kuppitz
{{PathRetractionStrategy}} should not be applied recursively, if possible. This
is considered an anti-pattern and just recently it caused a lot of trouble.
This commit fixed the recent issue:
https://github.com/apache/tinkerpop/commit/b8eb8a02f1675a1b22b86ccc54d22453c65f406f
{{PathRetractionStrategy}} collects requirements of child traversals, before
other strategies have a chance to mutate them. When other strategies get to the
child traversals, mutate them and thus add or remove requirements, a few things
can go crazy, especially because traverser requirements get cached when they're
first requested.
Since I do not fully understand the {{PathRetractionStrategy}} code, my fix was
actually a workaround. As you can see in the commit linked above, I implemented
the same anti-pattern in {{SubgraphStrategy}} and
{{IncidentToAdjacentStrategy}}; these are the 2 strategies that can potentially
change the traverser requirements.
It would be nice to revert these changes and instead make
{{PathRetractionStrategy}} work like all others. However, I'm not sure if
that's even possible.
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