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https://issues.apache.org/jira/browse/PIG-3648?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13863684#comment-13863684
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Matt Bossenbroek commented on PIG-3648:
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I came across this issue while trying to order data with a large number of
reducers. The last reducer ended up with 10x the data of the other reducers and
took 10x longer to execute.
I ran some statistical simulations on the selection algo and found that with a
small sample size, the likelihood of a less than uniform sample distribution
was higher. In my example, it was selecting only 100 rows out of 13M, which
wasn't representative of the data.
I can provide the sample code I was using to test this if needed.
> Make the sample size for RandomSampleLoader configurable
> --------------------------------------------------------
>
> Key: PIG-3648
> URL: https://issues.apache.org/jira/browse/PIG-3648
> Project: Pig
> Issue Type: Improvement
> Components: impl
> Reporter: Cheolsoo Park
> Assignee: Cheolsoo Park
> Priority: Minor
> Fix For: 0.13.0
>
> Attachments: PIG-3648-1.patch
>
>
> Pig uses RandomSampleLoader for range partitioning in order-by. But since the
> sample size is hardcoded as 100, volatility in the variance of the results
> increases when sorting a large number of rows (e.g. 10M+ per task).
> It would be nice if the sample size could be configurable via Pig properties.
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