bruno-roustant commented on a change in pull request #1043: LUCENE-9071: Speed
up BM25 scores.
URL: https://github.com/apache/lucene-solr/pull/1043#discussion_r352157819
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File path:
lucene/core/src/java/org/apache/lucene/search/similarities/BM25Similarity.java
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@@ -221,8 +251,8 @@ public final SimScorer scorer(float boost,
CollectionStatistics collectionStats,
@Override
public float score(float freq, long encodedNorm) {
- double norm = cache[((byte) encodedNorm) & 0xFF];
- return weight * (float) (freq / (freq + norm));
+ float norm = cache[((byte) encodedNorm) & 0xFF];
+ return weight * tf(freq, norm);
Review comment:
As I understand, this is the line that optimizes. Indeed casts to double and
then to float cost. I'm surprised that it matters on the overall query
throughput. It is in the order of a couple of ns, so the impact is visible for
lots of scores (millions), yes.
If freq, norm and score were double, then we wouldn't have casts and the
speed would be the good one on 64 bits machines and we wouldn't need this
optimization. Could this API be changed in 9.x to have double instead of float?
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