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Posted to issues@spark.apache.org by "Andrew Duffy (JIRA)" <ji...@apache.org> on 2016/08/24 11:56:20 UTC
[jira] [Updated] (SPARK-17213) Parquet String Pushdown for Non-Eq
Comparisons Broken
[ https://issues.apache.org/jira/browse/SPARK-17213?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Andrew Duffy updated SPARK-17213:
---------------------------------
Description:
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.
Link to PARQUET issue: https://issues.apache.org/jira/browse/PARQUET-686
Link to PR: https://github.com/apache/parquet-mr/pull/362
was:
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.
> 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.
> Link to PARQUET issue: https://issues.apache.org/jira/browse/PARQUET-686
> Link to PR: https://github.com/apache/parquet-mr/pull/362
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