[jira] [Updated] (SPARK-18479) spark.sql.shuffle.partitions defaults should be a prime number

["Sean Owen (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SPARK-18479?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Sean Owen updated SPARK-18479:
------------------------------
      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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