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runnable with provided script calculate_average_obourgain.sh (#75)
Runs with standard JDK 21.
On my computers (i5 13500, 20 cores, 32GB ram) my best run is (file fully in page cache):
49.78user 0.69system 0:02.81elapsed 1795%CPU
A bit older version of the code on Mac pro M1 32 GB:
real 0m2.867s
user 0m23.956s
sys 0m1.329s
As I wrote in comments in the code, I have a few different roundings that the reference implementation. I have seend that there is an issue about that, but no specific rule yet.
Main points:
- use MemorySegment, it's faster than ByteBuffer
- split the work in a lot of chunks and distribute to a thread pool
- fast measurement parser by using a lot of domain knowledge
- very low allocation
- visit each byte only once
Things I tried that were in fact pessimizations:
- use some internal JDK code to vectorize the hashCode computation
- use a MemorySegment to represent the keys instead of byte[], to avoid
copying
Hope I won't have a bad surprise when running on the target server 😱
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