Github user HyukjinKwon commented on a diff in the pull request:
https://github.com/apache/spark/pull/17395#discussion_r107822893
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/FileFormatWriter.scala
---
@@ -292,7 +292,10 @@ object FileFormatWriter extends Logging {
override def execute(iter: Iterator[InternalRow]): Set[String] = {
var fileCounter = 0
var recordsInFile: Long = 0L
- newOutputWriter(fileCounter)
+ // Skip the empty partition to avoid creating a mass of 'empty'
files.
+ if (iter.hasNext) {
+ newOutputWriter(fileCounter)
--- End diff --
Yes, I was thinking in that way. I remember I tried several tries at that
time but failed to make a good fix, and could not have some time to work on
that further.
Another problem is, it might be a datasource-specific issue because, for
example, ORC does not write out empty df. For example,
```
scala> spark.range(100).filter("id > 100").write.orc("/tmp/abc1")
scala> spark.read.orc("/tmp/abc1").show()
org.apache.spark.sql.AnalysisException: Unable to infer schema for ORC. It
must be specified manually.;
at
org.apache.spark.sql.execution.datasources.DataSource$$anonfun$8.apply(DataSource.scala:182)
at
org.apache.spark.sql.execution.datasources.DataSource$$anonfun$8.apply(DataSource.scala:182)
```
This issue is described in
https://issues.apache.org/jira/browse/SPARK-15474.
FWIW, I happened to see https://issues.apache.org/jira/browse/SPARK-15693
around that time and I kind of felt we may be able to consolidate this issue
with it although it is a rough idea.
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