[GitHub] [pinot] richardstartin edited a comment on pull request #7487: use MethodHandle to access vectorized unsigned comparison on JDK9+

[GitBox <gi...@apache.org>]

richardstartin edited a comment on pull request #7487:
URL: https://github.com/apache/pinot/pull/7487#issuecomment-927795364


   Here's a quick comparison to show what's at stake here (I don't think the benchmark is worth maintaining in this project). Note that I selected lengths which aren't aligned to make sure slower tail loops execute, which won't happen on aligned inputs.
   
   ```java
   @State(Scope.Benchmark)
   public class BenchmarkByteArrayCompare {
   
     @Param({"7", "31", "1023"})
     int _length;
   
     @Param("1")
     int _offset;
   
     private byte[] _left;
     private byte[] _right;
   
     @Setup(Level.Trial)
     public void setup() {
       _left = new byte[_length];
       ThreadLocalRandom.current().nextBytes(_left);
       _right = Arrays.copyOf(_left, _left.length);
       _right[_right.length - _offset] = (byte) ~_left[_left.length - _offset];
     }
   
     @Benchmark
     public int compare() {
       return ByteArray.compare(_left, _right);
     }
   }
   ```
   
   
   ```
   Benchmark                          (_length)  (_offset)  Mode  Cnt    Score   Error  Units
   BenchmarkByteArrayCompare.compare          7          1  avgt    5    5.942 ± 0.048  ns/op
   BenchmarkByteArrayCompare.compare         31          1  avgt    5   15.298 ± 1.040  ns/op
   BenchmarkByteArrayCompare.compare       1023          1  avgt    5  320.390 ± 1.262  ns/op
   
   Benchmark                          (_length)  (_offset)  Mode  Cnt   Score   Error  Units
   BenchmarkByteArrayCompare.compare          7          1  avgt    5   7.913 ± 0.174  ns/op
   BenchmarkByteArrayCompare.compare         31          1  avgt    5   8.351 ± 0.016  ns/op
   BenchmarkByteArrayCompare.compare       1023          1  avgt    5  22.765 ± 1.566  ns/op
   ```
   
   For inputs shorter than 8 bytes, there is a small setup cost of the order of 1ns, but for larger inputs the improvement is huge. 


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