Github user cloud-fan commented on a diff in the pull request:
https://github.com/apache/spark/pull/19623#discussion_r148239331
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/sources/v2/reader/ReadTask.java ---
@@ -37,13 +37,19 @@
* The preferred locations where this read task can run faster, but
Spark does not guarantee that
* this task will always run on these locations. The implementations
should make sure that it can
* be run on any location. The location is a string representing the
host name of an executor.
+ *
+ * If an exception was thrown, the action would fail and we guarantee
that no Spark job was
+ * submitted.
*/
default String[] preferredLocations() {
return new String[0];
--- End diff --
for `independent-of-location placement`, users can just return `new
String[0]`.
I don't know where Spark treats "localhost" as "anywhere", but I'd expect
it to be an unrecognized host and then it's "anywhere".
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