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Posted to issues@lucene.apache.org by "vignesh9727 (via GitHub)" <gi...@apache.org> on 2026/06/01 07:34:30 UTC
[PR] Fix OffHeapFloatVectorValues#prefetch to use bounded ord count [lucene]
vignesh9727 opened a new pull request, #16156:
URL: https://github.com/apache/lucene/pull/16156
`OffHeapFloatVectorValues#prefetch` computes `finalNumOrds = Math.min(numOrds, ordsToPrefetch.length)` and uses it for the early-return guard, but then loops over `numOrds` instead of `finalNumOrds`. The byte counterpart `OffHeapByteVectorValues#prefetch` correctly loops over `finalNumOrds`.
Since callers (e.g. `PrefetchableFlatVectorScorer`) pass a reused scratch array, `numOrds` can be smaller than the array length — the float path then prefetches stale ordinals from previous calls. If `numOrds` ever exceeded the array length, the loop would also go out of bounds (which `finalNumOrds` exists to prevent).
One-line fix to match the byte implementation.
Introduced in #15722.
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This is a trivial fix — a `skip-changelog` label may be appropriate.
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Re: [PR] Fix OffHeapFloatVectorValues#prefetch to use bounded ord count [lucene]
Posted by "vignesh9727 (via GitHub)" <gi...@apache.org>.
vignesh9727 commented on PR #16156:
URL: https://github.com/apache/lucene/pull/16156#issuecomment-4599483278
Hi @mikemccand The changelog entry is added and CI is fully green. Could you take a look when you have a moment?
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Re: [PR] Fix OffHeapFloatVectorValues#prefetch to use bounded ord count [lucene]
Posted by "vignesh9727 (via GitHub)" <gi...@apache.org>.
vignesh9727 commented on PR #16156:
URL: https://github.com/apache/lucene/pull/16156#issuecomment-4604016471
@benwtrent Added testPrefetchBoundedByArrayLength in `TestOffHeapVectorValues.java`. Passes an array of length 2 with numOrds=5 and asserts only 2 prefetches happen — this would throw ArrayIndexOutOfBoundsException on the old code. All three test pass locally..
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Re: [PR] Fix OffHeapFloatVectorValues#prefetch to use bounded ord count [lucene]
Posted by "benwtrent (via GitHub)" <gi...@apache.org>.
benwtrent commented on PR #16156:
URL: https://github.com/apache/lucene/pull/16156#issuecomment-4603146569
@vignesh9727 please add a test to lucene/core/src/test/org/apache/lucene/codecs/lucene95/TestOffHeapVectorValues.java
Obviously something was missed, it seems we need a test that ensures only `numOrds` is prefetched instead of the entire array every time.
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Re: [PR] Fix OffHeapFloatVectorValues#prefetch to use bounded ord count [lucene]
Posted by "benwtrent (via GitHub)" <gi...@apache.org>.
benwtrent merged PR #16156:
URL: https://github.com/apache/lucene/pull/16156
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