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https://issues.apache.org/jira/browse/LUCENE-9583?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17231499#comment-17231499
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Michael Sokolov commented on LUCENE-9583:
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bq. Perhaps we could revisit this issue once the first ANN implementation is
completed?
[~jtibshirani] that makes sense. We can leave this open, even though the
attached PR was pushed. I just pushed LUCENE-9004 as well, implementing NSW
graph indexing, so that should give us a more concrete basis for comparison. I
have been testing performance (recall/latency) using a KnnGraphTester class
that is part of that. However one challenge is coming up with a test dataset we
can share. I have been using some proprietary embeddings, getting good results,
and just started looking into testing with GloVe, and got not-so-good results
there. I am concerned that GloVe may have some strong clustering and require
us to implement the diversity heuristic from the HNSW paper.
> 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: 20m
> 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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