[jira] [Resolved] (IMPALA-10323) use snprintf instead of lexical_cast when casting int to string, to improve multi-thread performance

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

     [ https://issues.apache.org/jira/browse/IMPALA-10323?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

wesleydeng resolved IMPALA-10323.
---------------------------------
    Fix Version/s: Impala 4.0
       Resolution: Fixed

> use snprintf instead of lexical_cast when casting int to string,  to improve multi-thread performance
> -----------------------------------------------------------------------------------------------------
>
>                 Key: IMPALA-10323
>                 URL: https://issues.apache.org/jira/browse/IMPALA-10323
>             Project: IMPALA
>          Issue Type: Improvement
>          Components: Backend
>    Affects Versions: Impala 3.1.0, Impala 3.2.0, Impala 3.3.0, Impala 3.4.0
>         Environment: 3 nodes ( 24 core, 64 GB mem)
> impala 3.4
>            Reporter: wesleydeng
>            Assignee: wesleydeng
>            Priority: Major
>             Fix For: Impala 4.0
>
>         Attachments: image-2020-11-12-20-36-50-082.png, image-2020-11-12-20-43-47-010.png
>
>   Original Estimate: 12h
>  Remaining Estimate: 12h
>
> For float_type, lexical_cast is replace by snprintf （issue https://issues.apache.org/jira/browse/IMPALA-1738），but why not do the same replacement for num_type.
> Test is done in 2 sql case :
> 1)  *group by cast int to string* : 
> select cast(f1 as string) as kk, count ( * ) from test.my_table group by kk;
> 2) *group by* *int :* 
> select f1 as kk, count( *  ) from test.my_table  group by kk;
> !image-2020-11-12-20-43-47-010.png!
> from the benchmark, we can see that performance decreased seriously with more thread.
> But using snprintf, performance improved significantly with more thread .
>  



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