GitHub user HyukjinKwon opened a pull request:
https://github.com/apache/spark/pull/17680
[SPARK-20364][SQL] Support Parquet predicate pushdown on columns with dots
## What changes were proposed in this pull request?
Currently, if there are dots in the column name, predicate pushdown seems
being failed in Parquet.
**With dots**
```
val path = "/tmp/abcde"
Seq(Some(1), None).toDF("col.dots").write.parquet(path)
spark.read.parquet(path).where("`col.dots` IS NOT NULL").show()
```
```
+--------+
|col.dots|
+--------+
+--------+
```
**Without dots**
```
val path = "/tmp/abcde"
Seq(Some(1), None).toDF("coldots").write.parquet(path)
spark.read.parquet(path).where("`coldots` IS NOT NULL").show()
```
```
+-------+
|coldots|
+-------+
| 1|
+-------+
```
It seems dot in the column names via `FilterApi` tries to separate the
field name with dot (`ColumnPath` with multiple column paths) whereas the
actual column name is `col.dots`. (See
[FilterApi.java#L71](https://github.com/apache/parquet-mr/blob/apache-parquet-1.8.2/parquet-column/src/main/java/org/apache/parquet/filter2/predicate/FilterApi.java#L71)
and it calls
[ColumnPath.java#L44](https://github.com/apache/parquet-mr/blob/apache-parquet-1.8.2/parquet-common/src/main/java/org/apache/parquet/hadoop/metadata/ColumnPath.java#L44).
I just tried to come up with ways to resolve it and I came up with two as
below:
- One is simply to don't push down filters when there are dots in column
names so that it reads all and filters in Spark-side.
- The other way creates Spark's `FilterApi` for those columns (it seems
final) to get always use single column path it in Spark-side (this seems hacky)
as we are not pushing down nested columns currently. So, it looks we can get a
field name via `ColumnPath.get` not `ColumnPath.fromDotString` in this way.
This PR proposes the latter way because I think we need to be sure on that
it passes the tests.
**After**
```scala
val path = "/tmp/abcde"
Seq(Some(1), None).toDF("col.dots").write.parquet(path)
spark.read.parquet(path).where("`col.dots` IS NOT NULL").show()
```
```
+--------+
|col.dots|
+--------+
| 1|
+--------+
```
## How was this patch tested?
Existing tests should cover this. Some tests additionally were added in
`ParquetFilterSuite.scala`. Manually, I ran related tests and Jenkins tests
will cover this.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/HyukjinKwon/spark SPARK-20364
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/spark/pull/17680.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #17680
----
commit 297c70bd47cb859d343345849776bd7c21396078
Author: hyukjinkwon <gurwls...@gmail.com>
Date: 2017-04-19T06:24:15Z
Parquet predicate pushdown on columns with dots return empty results
----
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