Hamel Ajay Kothari created SPARK-18479:
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Summary: 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: Bug
Components: SQL
Affects Versions: 2.0.2
Reporter: Hamel Ajay Kothari
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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