[jira] [Updated] (FLINK-23555) Improve common subexpression elimination by using local references

["Yun Gao (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-23555?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Yun Gao updated FLINK-23555:
----------------------------
    Fix Version/s: 1.16.0

> Improve common subexpression elimination by using local references
> ------------------------------------------------------------------
>
>                 Key: FLINK-23555
>                 URL: https://issues.apache.org/jira/browse/FLINK-23555
>             Project: Flink
>          Issue Type: Bug
>          Components: Table SQL / Planner
>            Reporter: weibowen
>            Priority: Major
>             Fix For: 1.15.0, 1.16.0
>
>         Attachments: performance_after_optimization.png, performance_before_optimization.png, sql.png, udf.png
>
>
> When we write a sql like 
> {code:java}
> select udf2(udf1(field), udf3(udf1(field) ...{code}
> 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,
> !sql.png!
> 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.
> !udf.png!
> As expected, the performance after optimization is approximately 3 times than before since I write `testcse(sid)` 3 times in sql.
> before:
> !performance_before_optimization.png!
> after:
> !performance_after_optimization.png!
>  



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