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From "Alan Woodward (JIRA)" <>
Subject [jira] [Updated] (LUCENE-7736) Expose some IndexReader stats via DoubleValuesSources
Date Mon, 10 Apr 2017 08:15:41 GMT


Alan Woodward updated LUCENE-7736:
    Attachment: LUCENE-7736.patch

I tried a few different ways of making these sources immutable, including holding a weak hashmap
of reader ids on them, but in the end I think the cleanest API is to have a rewrite(IndexReader)
method on Double/LongValuesSource.  This requires a couple of changes elsewhere in the codebase
- we already have a Sort.rewrite() method, but it wasn't being called by IndexSearcher or
SortRescorer, for example - but I think ends up with things being neater.

I removed norms() and joinDocFreq(); all int-valued IndexReader methods now return a DoubleValuesSource,
as an int can fit into a double with no loss of precision.  IndexReaderFunctions.sumTotalTermFreq()
returns a LongValuesSource, as it delegates to a long-valued function.  If a user wants to
use this in an expression, or similar, then they'll need to explicitly cast using .toDoubleValuesSource().

A nice extra feature here would be to wrap these up in a Bindings implementation for the expressions
module, which would require moving back into core, but that's for a follow-up issue, I think.

> Expose some IndexReader stats via DoubleValuesSources
> -----------------------------------------------------
>                 Key: LUCENE-7736
>                 URL:
>             Project: Lucene - Core
>          Issue Type: New Feature
>            Reporter: Alan Woodward
>            Assignee: Alan Woodward
>            Priority: Minor
>         Attachments: LUCENE-7736.patch, LUCENE-7736.patch
> We have a number of ValueSource implementations that expose IndexReader stats (numDocs,
termFreq, etc).  We should re-implement these as DoubleValuesSources, allowing them to be
used in FunctionScoreQuery, etc.

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