chishui commented on code in PR #16836:
URL: https://github.com/apache/lucene/pull/16836#discussion_r4310951528
##########
lucene/core/src/java/org/apache/lucene/util/compress/LZ4.java:
##########
@@ -147,6 +147,95 @@ public static int decompress(DataInput compressed, int
decompressedLen, byte[] d
return dOff;
}
+ /**
+ * Same as {@link #decompress(DataInput, int, byte[], int)}, but reads the
compressed bytes from
+ * {@code compressed[cOff:cOff+cLen]}. Reading from a heap array avoids the
per-byte overhead of
+ * {@link DataInput#readByte()}, which dominates decompression when the
input is an {@code
+ * IndexInput}.
+ */
+ public static int decompress(
Review Comment:
I ran a benchmark and the performance of using `ByteArrayDataInput` is worse
```
┌────────────────────┬───────────────┬────────────────────┬─────────────────────────────────┐
│ docType │ benchmark │ ByteArrayDataInput │
ByteArrayDataInput & IndexInput │
├────────────────────┼───────────────┼────────────────────┼─────────────────────────────────┤
│ text │ randomAccess │ +6.8% │ +15.6% (223.6 →
258.5 µs) │
├────────────────────┼───────────────┼────────────────────┼─────────────────────────────────┤
│ text │ mergeInstance │ +1.2% │ +14.0%
│
├────────────────────┼───────────────┼────────────────────┼─────────────────────────────────┤
│ sparse_vector_json │ randomAccess │ +5.7% │ +20.3% (334.2 →
402.1 µs) │
├────────────────────┼───────────────┼────────────────────┼─────────────────────────────────┤
│ sparse_vector_json │ mergeInstance │ +6.1% │ +18.4%
│
└────────────────────┴───────────────┴────────────────────┴─────────────────────────────────┘
note: LZ4.decompress(DataInput) also decodes blocktree terms and doc values
from an IndexInput
```
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