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https://issues.apache.org/jira/browse/LUCENE-10404?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17570195#comment-17570195
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Michael Sokolov commented on LUCENE-10404:
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The default `topK` in KnnGraphTester is 100, so these test runs are maintaining
results queues of 100 or 150 (when searching). During indexing this is driven
by beamWidth, and 32/64 is lower than is typical, I think. Still I think it's
encouraging that we see gains in both searching (when the queue size is
100-150) and indexing, when it is 32-64.
I won't be able to run more tests for a few days, but I agree that it would be
interesting to see how the gains correlate with the queue sizes. But I was
motivated to get some quick look! Will run some more exhaustive tests next week.
> Use hash set for visited nodes in HNSW search?
> ----------------------------------------------
>
> Key: LUCENE-10404
> URL: https://issues.apache.org/jira/browse/LUCENE-10404
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Julie Tibshirani
> Priority: Minor
>
> While searching each layer, HNSW tracks the nodes it has already visited
> using a BitSet. We could look into using something like IntHashSet instead. I
> tried out the idea quickly by switching to IntIntHashMap (which has already
> been copied from hppc) and saw an improvement in index performance.
> *Baseline:* 760896 msec to write vectors
> *Using IntIntHashMap:* 733017 msec to write vectors
> I noticed search performance actually got a little bit worse with the change
> -- that is something to look into.
> For background, it's good to be aware that HNSW can visit a lot of nodes. For
> example, on the glove-100-angular dataset with ~1.2 million docs, HNSW search
> visits ~1000 - 15,000 docs depending on the recall. This number can increase
> when searching with deleted docs, especially if you hit a "pathological" case
> where the deleted docs happen to be closest to the query vector.
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