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  1. Flink
  2. FLINK-23555

Improve common subexpression elimination by using local references

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    Details

    • Type: Bug
    • Status: Open
    • Priority: Major
    • Resolution: Unresolved
    • Affects Version/s: None
    • Fix Version/s: 1.14.0
    • Component/s: Table SQL / Planner
    • Labels:
      None

      Description

      When we write a sql like 

      select udf2(udf1(field), udf3(udf1(field) ...

      udf1(field) will be invoked twice. However once udf1 has a bad performance, it will have a huge impact to the whole task. More times invoked, huger impact.

      I hope that whatever how many times udf1(field) writed in sql, Flink will take advantage of common subexpression elimination and only invoke it once.

      Then i do some work on this, and the attachment tells the result.

       

      The sql.png shows the sql logic,

      and i read source from kafka and sink into blackhole. The parallelism is 1.

      The udf `testcse` do nothing except sleeping 20 milliseconds, while the udf `testcse2`, `testcse3` and `testcse4` are the same udf with different alias which completely do nothing.

      As expected, the performance after optimization is approximately 3 times than before since I write `testcse(sid)` 3 times in sql.

      before:

      after:

       

        Attachments

        1. udf.png
          13 kB
          weibowen
        2. sql.png
          17 kB
          weibowen
        3. performance_before_optimization.png
          34 kB
          weibowen
        4. performance_after_optimization.png
          33 kB
          weibowen

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            • Assignee:
              Unassigned
              Reporter:
              b0o0wen weibowen
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              Dates

              • Created:
                Updated: