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Posted to issues@spark.apache.org by "tomzhu (JIRA)" <ji...@apache.org> on 2019/02/16 11:08:00 UTC
[jira] [Created] (SPARK-26899) CountMinSketchAgg
ExpressionDescription is not so correct
tomzhu created SPARK-26899:
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Summary: CountMinSketchAgg ExpressionDescription is not so correct
Key: SPARK-26899
URL: https://issues.apache.org/jira/browse/SPARK-26899
Project: Spark
Issue Type: Documentation
Components: SQL
Affects Versions: 2.4.0
Reporter: tomzhu
Hi, all, there are some not-so-correct comment in CountMinSketchAgg.scala, the ExpressionDescription says:
{code:java}
@ExpressionDescription(
usage = """
_FUNC_(col, eps, confidence, seed) - Returns a count-min sketch of a column with the given esp,
confidence and seed. The result is an array of bytes, which can be deserialized to a
`CountMinSketch` before usage. Count-min sketch is a probabilistic data structure used for
cardinality estimation using sub-linear space.
""",
since = "2.2.0")
{code}
, *the Count-min sketch is a probabilistic data structure used for cardinality estimation*, ** actually, Count-min sketch is mainly used for point query, self_join size query,
how can it support cardinality estimation? a fix might be better.
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