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https://issues.apache.org/jira/browse/LUCENE-8574?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17148963#comment-17148963
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Michael McCandless commented on LUCENE-8574:
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[~zhai7631] does this fix your combinatoric adversarial test case
({{testFibonacciExpr}})?
I.e. before the fix, that test runs for way too long (days), but after, it runs
quickly?
I left some small comments on the PR. Thanks for tackling this!
> ExpressionFunctionValues should cache per-hit value
> ---------------------------------------------------
>
> Key: LUCENE-8574
> URL: https://issues.apache.org/jira/browse/LUCENE-8574
> Project: Lucene - Core
> Issue Type: Bug
> Affects Versions: 7.5, 8.0
> Reporter: Michael McCandless
> Assignee: Robert Muir
> Priority: Major
> Attachments: LUCENE-8574.patch, unit_test.patch
>
> Time Spent: 1h 20m
> Remaining Estimate: 0h
>
> The original version of {{ExpressionFunctionValues}} had a simple per-hit
> cache, so that nested expressions that reference the same common variable
> would compute the value for that variable the first time it was referenced
> and then use that cached value for all subsequent invocations, within one
> hit. I think it was accidentally removed in LUCENE-7609?
> This is quite important if you have non-trivial expressions that reference
> the same variable multiple times.
> E.g. if I have these expressions:
> {noformat}
> x = c + d
> c = b + 2
> d = b * 2{noformat}
> Then evaluating x should only cause b's value to be computed once (for a
> given hit), but today it's computed twice. The problem is combinatoric if b
> then references another variable multiple times, etc.
> I think to fix this we just need to restore the per-hit cache?
>
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