Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/12247#discussion_r59255827
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/DataSource.scala
---
@@ -123,8 +123,16 @@ case class DataSource(
}
}
- /** Returns a source that can be used to continually read data. */
- def createSource(): Source = {
+ /**
+ * Returns a source that can be used to continually read data.
+ *
+ * Before running a real query (e.g., df.explain), `sourceId` and
`checkpointLocation` is None
+ * as they are unknown. [[ContinuousQueryManager]] should set `sourceId`
and `checkpointLocation`
+ * before starting a query.
+ */
+ def createSource(
+ sourceId: Option[Long] = None,
+ checkpointLocation: Option[String] = None): Source = {
--- End diff --
Yeah, and we also don't really need to create a source there (we only need
to know the schema). Perhaps getting the schema should be separated from
getting the source (like we do in FileFormat).
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