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Posted to issues@spark.apache.org by "Apache Spark (JIRA)" <ji...@apache.org> on 2019/03/08 03:13:00 UTC
[jira] [Assigned] (SPARK-27099) Expose xxHash64 as a flexible
64-bit column hash like `hash`
[ https://issues.apache.org/jira/browse/SPARK-27099?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Apache Spark reassigned SPARK-27099:
------------------------------------
Assignee: (was: Apache Spark)
> Expose xxHash64 as a flexible 64-bit column hash like `hash`
> ------------------------------------------------------------
>
> Key: SPARK-27099
> URL: https://issues.apache.org/jira/browse/SPARK-27099
> Project: Spark
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 2.3.3, 2.4.0
> Reporter: Huon Wilson
> Priority: Major
>
> I’m working on something that requires deterministic randomness, i.e. a row gets the same “random” value no matter the order of the DataFrame. A seeded hash seems to be the perfect way to do this, but the existing hashes have various limitations:
> - hash: 32-bit output (only 4 billion possibilities will result in a lot of collisions for many tables: the birthday paradox implies >50% chance of at least one for tables larger than 77000 rows, and likely ~1.6 billion collisions in a table of size 4 billion)
> - sha1/sha2/md5: single binary column input, string output
> It seems there’s already support for a 64-bit hash function that can work with an arbitrary number of arbitrary-typed columns (XxHash64), which could be exposed as xxHash64 or xxhash64 (or similar).
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