benwtrent commented on issue #14763:
URL: https://github.com/apache/lucene/issues/14763#issuecomment-2956287088
```
8.63% 382600 java.util.Arrays#fill() [Inlined code]
at org.apache.lucene.util.FixedBitSet#clear()
[Inlined code]
at
org.apache.lucene.util.hnsw.HnswGraphSearcher#prepareScratchState() [Inlined
code]
at
org.apache.lucene.util.hnsw.HnswGraphSearcher#searchLevel() [JIT compiled code]
```
The main caller for `prepareScratchState` is during graph building. However,
we will clear the bit set between finding the best entry point and searching
the bottom layer. So, it *SHOULD* only be called twice per segment, no matter
then graph size.
The question that leaves two questions:
- "Do we need to clear the bitset between finding the entry point and
search layer 0 at search time" and honestly, since we only do it twice, I think
keeping it in is fine. My concern would be if we actually have to span our
further due to result filtering, we might actually miss nearest neighbors that
were explored on previous levels.
- "Do we need to clear the bitset during index building". This one is
trickier. I think there is some optimization we can do here as by definition,
the entrypoint we find at a layer is the nearest vector and all previously
explored vectors at previous layers are further away.
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