[jira] [Resolved] (SPARK-15680) Disable comments in generated code in order to avoid performance issues

["Reynold Xin (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-15680?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Reynold Xin resolved SPARK-15680.
---------------------------------
       Resolution: Fixed
    Fix Version/s: 2.0.0

> Disable comments in generated code in order to avoid performance issues
> -----------------------------------------------------------------------
>
>                 Key: SPARK-15680
>                 URL: https://issues.apache.org/jira/browse/SPARK-15680
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>            Reporter: Josh Rosen
>            Assignee: Josh Rosen
>             Fix For: 2.0.0
>
>         Attachments: pasted_image_at_2016_05_29_03_02_pm.png, pasted_image_at_2016_05_29_03_03_pm.png
>
>
> In benchmarks involving tables with very wide and complex schemas (thousands of columns, deep nesting), I noticed that significant amounts of time (order of tens of seconds per task) were being spent generating comments during the code generation phase.
> The root cause of the performance problem stems from the fact that calling {{toString()}} on a complex expression can involve thousands of string concatenations, resulting in huge amounts (tens of gigabytes) of character array allocation and copying (see attached profiler screenshots)
> In the long term, we can avoid this problem by passing StringBuilders down the tree and using them to accumulate output. In the short term, however, I think that we should just disable comments in the generated code by default since very long comments are typically not useful debugging aids (since they're truncated for display anyways).



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