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https://issues.apache.org/jira/browse/LUCENE-9395?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17128876#comment-17128876
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David Smiley commented on LUCENE-9395:
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Hello! {{org.apache.lucene.search.DoubleValuesSource#getValues}} is called
about once per segment, and so it's not an allocation hotspot. There are tons
of implementations of this method and similarly for
{{org.apache.lucene.search.Weight#scorer}} as well which is also called about
once per segment that typically allocate a bunch of stuff. I don't think it's
worth bothering changing the code. There is a very slight help for the GC
(that I doubt you could even measure) and a very slight negative impact on
complexity.
> ConstantValuesSource creates more than one DoubleValues unnecessarily
> ----------------------------------------------------------------------
>
> Key: LUCENE-9395
> URL: https://issues.apache.org/jira/browse/LUCENE-9395
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/search
> Affects Versions: 8.5.2
> Reporter: Tony Xu
> Priority: Minor
> Attachments: LUCENE-9395.patch
>
>
> At my day job, we use ConstantValuesSource to represent default values or a
> constant query-level feature by calling *_DoubleValuesSource.constant_*. I
> realized under the hood the _*ConstantValuesSource.getDoubleValues*_ creates
> a new _*DoubleValues*_ which simply return the specified value each time it
> is called.
> Unless I missed something, I don't see a risk of creating one
> _*DoubleValues*_ as use it as the return value of all _*getDoubleValues**()*_
> calls given that the constant _*DoubleValues*_ doesn't maintain any state.
> We can also offer the user flexibilities of how to initialize it.
> 1) _*DoubleValuesSource.constant(double constant)*_ – we can eagerly
> initialize an `DoubleValues` that returns the constant and make it the return
> value of all _*getDoubleValues()*_ calls.
> 2) _*DoubleValuesSource.constant(DoubleSupplier doubleSupplier)*_ – For lazy
> evaluation if the constant takes some time to compute and user expects the
> returned DVS will not be used in all code path.
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