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https://issues.apache.org/jira/browse/LUCENE-9583?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17221445#comment-17221445
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Michael Sokolov commented on LUCENE-9583:
-----------------------------------------

The attached PR follows up on the idea of splitting out RandomAccess into a 
pair of new top-level interfaces: RandomAccessVectorValues and 
RandomAccessVectorValuesProducer. I think it will help with making the public 
API clearer. Is there a blessed way to mark such interfaces as 
internal-use-only, even though they must be public in order to be visible 
across packages internally?

> How should we expose VectorValues.RandomAccess?
> -----------------------------------------------
>
>                 Key: LUCENE-9583
>                 URL: https://issues.apache.org/jira/browse/LUCENE-9583
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Michael Sokolov
>            Priority: Major
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> In the newly-added {{VectorValues}} API, we have a {{RandomAccess}} 
> sub-interface. [~jtibshirani] pointed out this is not needed by some 
> vector-indexing strategies which can operate solely using a forward-iterator 
> (it is needed by HNSW), and so in the interest of simplifying the public API 
> we should not expose this internal detail (which by the way surfaces internal 
> ordinals that are somewhat uninteresting outside the random access API).
> I looked into how to move this inside the HNSW-specific code and remembered 
> that we do also currently make use of the RA API when merging vector fields 
> over sorted indexes. Without it, we would need to load all vectors into RAM  
> while flushing/merging, as we currently do in 
> {{BinaryDocValuesWriter.BinaryDVs}}. I wonder if it's worth paying this cost 
> for the simpler API.
> Another thing I noticed while reviewing this is that I moved the KNN 
> {{search(float[] target, int topK, int fanout)}} method from {{VectorValues}} 
>  to {{VectorValues.RandomAccess}}. This I think we could move back, and 
> handle the HNSW requirements for search elsewhere. I wonder if that would 
> alleviate the major concern here? 



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