Andrew Duffy created SPARK-17213:
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Summary: Parquet String Pushdown for Non-Eq Comparisons Broken
Key: SPARK-17213
URL: https://issues.apache.org/jira/browse/SPARK-17213
Project: Spark
Issue Type: Bug
Affects Versions: 2.0.0
Reporter: Andrew Duffy
Spark defines ordering over strings based on comparison of UTF8 byte arrays,
which compare bytes as unsigned integers. Currently however Parquet does not
respect this ordering. This is currently in the process of being fixed in
Parquet, JIRA and PR link below, but currently all filters are broken over
strings, with there actually being a correctness issue for {{>}} and {{<}}.
*Repro:*
Querying directly from in-memory DataFrame:
{code}
> Seq("a", "é").toDF("name").where("name > 'a'").count
1
{code}
Querying from a parquet dataset:
{code}
> Seq("a", "é").toDF("name").write.parquet("/tmp/bad")
> spark.read.parquet("/tmp/bad").where("name > 'a'").count
0
{code}
This happens because Spark sorts the rows to be {{[a, é]}}, but Parquet's
implementation of comparison of strings is based on signed byte array
comparison, so it will actually create 1 row group with statistics
{{min=é,max=a}}, and so the row group will be dropped by the query.
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