[jira] [Created] (SPARK-27099) Expose xxHash64 as a flexible 64-bit column hash like `hash`

["Huon Wilson (JIRA)" <ji...@apache.org>]

Huon Wilson created SPARK-27099:
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             Summary: 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: 2.4.0, 2.3.3
            Reporter: Huon Wilson


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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