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https://issues.apache.org/jira/browse/SPARK-18479?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sean Owen updated SPARK-18479:
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Priority: Minor (was: Major)
Issue Type: Improvement (was: Bug)
> spark.sql.shuffle.partitions defaults should be a prime number
> --------------------------------------------------------------
>
> Key: SPARK-18479
> URL: https://issues.apache.org/jira/browse/SPARK-18479
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.0.2
> Reporter: Hamel Ajay Kothari
> Priority: Minor
>
> For most hash bucketing use cases it is my understanding that a prime value,
> such as 199, would be a safer value than the existing value of 200. Using a
> non-prime value makes the likelihood of collisions much higher when the hash
> function isn't great.
> Consider the case where you've got a Timestamp or Long column with
> millisecond times at midnight each day. With the default value for
> spark.sql.shuffle.partitions, you'll end up with 120/200 partitions being
> completely empty.
> Looking around there doesn't seem to be a good reason why we chose 200 so I
> don't see a huge risk in changing it.
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