[jira] [Created] (HBASE-28256) Enhance ByteBufferUtils.readVLong to read 8 bytes at a time

["Becker Ewing (Jira)" <ji...@apache.org>]

Becker Ewing created HBASE-28256:
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             Summary: Enhance ByteBufferUtils.readVLong to read 8 bytes at a time
                 Key: HBASE-28256
                 URL: https://issues.apache.org/jira/browse/HBASE-28256
             Project: HBase
          Issue Type: Improvement
          Components: Performance
            Reporter: Becker Ewing
            Assignee: Becker Ewing
         Attachments: async-prof-rs-cpu.html

Currently, ByteBufferUtils.readVLong is used to decode rows in all data block encodings in order to read the memstoreTs field. For a data block encoding like prefix, ByteBufferUtils.readVLong can surprisingly occupy over 50% of the CPU time in BufferedEncodedSeeker.decodeNext (which can be quite a hot method in seek operations).

 

Since memstoreTs will typically require at least 6 bytes to store, we could look to vectorize the read path for readVLong to read 8 bytes at a time instead of a single byte at a time (like in https://issues.apache.org/jira/browse/HBASE-28025) in order to increase performance.

 

Attached is a CPU flamegraph of a region server process which shows that we spend a surprising amount of time in decoding rows from the DBE in ByteBufferUtils.readVLong.



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