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