Github user steveloughran commented on a diff in the pull request:
https://github.com/apache/spark/pull/19623#discussion_r148503478
--- Diff:
sql/core/src/main/java/org/apache/spark/sql/sources/v2/writer/DataSourceV2Writer.java
---
@@ -50,28 +53,34 @@
/**
* Creates a writer factory which will be serialized and sent to
executors.
+ *
+ * If this method fails (by throwing an exception), the action would
fail and no Spark job was
+ * submitted.
*/
DataWriterFactory<Row> createWriterFactory();
/**
* Commits this writing job with a list of commit messages. The commit
messages are collected from
- * successful data writers and are produced by {@link
DataWriter#commit()}. If this method
- * fails(throw exception), this writing job is considered to be failed,
and
- * {@link #abort(WriterCommitMessage[])} will be called. The written
data should only be visible
- * to data source readers if this method succeeds.
+ * successful data writers and are produced by {@link
DataWriter#commit()}.
+ *
+ * If this method fails (by throwing an exception), this writing job is
considered to to have been
+ * failed, and {@link #abort(WriterCommitMessage[])} would be called.
The state of the destination
+ * is undefined and @{@link #abort(WriterCommitMessage[])} may not be
able to deal with it.
*
* Note that, one partition may have multiple committed data writers
because of speculative tasks.
* Spark will pick the first successful one and get its commit message.
Implementations should be
--- End diff --
Having >1 committed writers is a failure of protocol. Speculation & failure
handling should allow >1 ready-to-commit writers, but only actually commit one.
That's where the stuff about writers reporting ready-to-commit & driver
tracking state of active tasks comes in.
What if a commit fails/commit operation times out or raises some other
error? Hadoop FileOutputFormat v1 commit can actually recover from a failed
task commit, v2 can't [Assumption: rename() is atomic and will fail if dest
path exists). Hence the `OutputCommitter.isRecoverySupported()` probe to tell
driver whether or not it can recover from a task commit which is perceived as
failing.
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