jpountz commented on a change in pull request #730: LUCENE-8868: New storing
strategy for BKD tree leaves with low cardinality
URL: https://github.com/apache/lucene-solr/pull/730#discussion_r295688457
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File path: lucene/core/src/java/org/apache/lucene/util/bkd/BKDWriter.java
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@@ -1028,17 +1035,43 @@ private void writeLeafBlockDocs(DataOutput out, int[]
docIDs, int start, int cou
DocIdsWriter.writeDocIds(docIDs, start, count, out);
}
- private void writeLeafBlockPackedValues(DataOutput out, int[]
commonPrefixLengths, int count, int sortedDim, IntFunction<BytesRef>
packedValues) throws IOException {
+ private void writeLeafBlockPackedValues(DataOutput out, int[]
commonPrefixLengths, int count, int sortedDim, IntFunction<BytesRef>
packedValues, int leafCardinality) throws IOException {
int prefixLenSum = Arrays.stream(commonPrefixLengths).sum();
if (prefixLenSum == packedBytesLength) {
// all values in this block are equal
out.writeByte((byte) -1);
- } else {
+ } else if (leafCardinality * (packedBytesLength - prefixLenSum + 2) <=
count * (packedBytesLength - prefixLenSum)) {
Review comment:
Am I reading it right that you are counting 2 for the vint? I think you
could make it 1 instead, the reasoning being that if you vints are 2 bytes on
average, then it means than your runs are very long (vint start using 2 bytes
when they are greater than 127) and so the sparse encoding is an obvious win.
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