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https://issues.apache.org/jira/browse/LUCENE-9395?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17130930#comment-17130930
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Tony Xu commented on LUCENE-9395:
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Thanks Atri and David for taking the time to respond and test the change.
I agree it's not a needle-moving change and the basic intention is to save some
cpu cycles with small amount of complexity added. A more advanced use case is
where the constant takes non-trivial amount of time to compute. In this case,
we would like to not pay that cost if the DVS is not used.
I'm preparing another patch and to lazily initialize the DVs. Let's see how
that goes.
> 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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