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https://issues.apache.org/jira/browse/TINKERPOP-1925?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16402032#comment-16402032
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Daniel Kuppitz commented on TINKERPOP-1925:
-------------------------------------------
A quick thought on this: What if {{PathRetractionStrategy}} would just find the
last child traversal and then only kick in when it's applied to this traversal?
Something like this:
{noformat}
apply(traversal) {
// collect all child traversals, starting from the root traversal
if (traversal != last child traversal in list) return;
// apply strategy to root traversal
}
{noformat}
Unfortunately, this child traversal scan has to be done over and over again, as
other strategies could change the result. However, it's just a scan not
involving any mutations, I don't think it would cost too much time.
> 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
> Priority: Major
>
> {{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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