[jira] [Created] (SPARK-26629) Error with multiple file stream in a query + restart on a batch that has no data for one file stream

["Tathagata Das (JIRA)" <ji...@apache.org>]

Tathagata Das created SPARK-26629:
-------------------------------------

             Summary: Error with multiple file stream in a query + restart on a batch that has no data for one file stream
                 Key: SPARK-26629
                 URL: https://issues.apache.org/jira/browse/SPARK-26629
             Project: Spark
          Issue Type: Bug
          Components: Structured Streaming
    Affects Versions: 2.4.0, 2.3.2, 2.3.1, 2.3.0, 2.4.1
            Reporter: Tathagata Das
            Assignee: Tathagata Das


When a streaming query has multiple file streams, and there is a batch where one of the file streams dont have data in that batch, then if the query has to restart from that, it will throw the following error.

{code}
java.lang.IllegalStateException: batch 1 doesn't exist
	at org.apache.spark.sql.execution.streaming.HDFSMetadataLog$.verifyBatchIds(HDFSMetadataLog.scala:300)
	at org.apache.spark.sql.execution.streaming.FileStreamSourceLog.get(FileStreamSourceLog.scala:120)
	at org.apache.spark.sql.execution.streaming.FileStreamSource.getBatch(FileStreamSource.scala:181)
	at org.apache.spark.sql.execution.streaming.MicroBatchExecution$$anonfun$org$apache$spark$sql$execution$streaming$MicroBatchExecution$$populateStartOffsets$2.apply(MicroBatchExecution.scala:294)
	at org.apache.spark.sql.execution.streaming.MicroBatchExecution$$anonfun$org$apache$spark$sql$execution$streaming$MicroBatchExecution$$populateStartOffsets$2.apply(MicroBatchExecution.scala:291)
	at scala.collection.Iterator$class.foreach(Iterator.scala:891)
	at scala.collection.AbstractIterator.foreach(Iterator.scala:1334)
	at scala.collection.IterableLike$class.foreach(IterableLike.scala:72)
	at org.apache.spark.sql.execution.streaming.StreamProgress.foreach(StreamProgress.scala:25)
	at org.apache.spark.sql.execution.streaming.MicroBatchExecution.org$apache$spark$sql$execution$streaming$MicroBatchExecution$$populateStartOffsets(MicroBatchExecution.scala:291)
	at org.apache.spark.sql.execution.streaming.MicroBatchExecution$$anonfun$runActivatedStream$1$$anonfun$apply$mcZ$sp$1.apply$mcV$sp(MicroBatchExecution.scala:178)
	at org.apache.spark.sql.execution.streaming.MicroBatchExecution$$anonfun$runActivatedStream$1$$anonfun$apply$mcZ$sp$1.apply(MicroBatchExecution.scala:175)
	at org.apache.spark.sql.execution.streaming.MicroBatchExecution$$anonfun$runActivatedStream$1$$anonfun$apply$mcZ$sp$1.apply(MicroBatchExecution.scala:175)
	at org.apache.spark.sql.execution.streaming.ProgressReporter$class.reportTimeTaken(ProgressReporter.scala:251)
	at org.apache.spark.sql.execution.streaming.StreamExecution.reportTimeTaken(StreamExecution.scala:61)
	at org.apache.spark.sql.execution.streaming.MicroBatchExecution$$anonfun$runActivatedStream$1.apply$mcZ$sp(MicroBatchExecution.scala:175)
	at org.apache.spark.sql.execution.streaming.ProcessingTimeExecutor.execute(TriggerExecutor.scala:56)
	at org.apache.spark.sql.execution.streaming.MicroBatchExecution.runActivatedStream(MicroBatchExecution.scala:169)
	at org.apache.spark.sql.execution.streaming.StreamExecution.org$apache$spark$sql$execution$streaming$StreamExecution$$runStream(StreamExecution.scala:295)
	at org.apache.spark.sql.execution.streaming.StreamExecution$$anon$1.run(StreamExecution.scala:205)
{code}

**Reason**
Existing {{HDFSMetadata.verifyBatchIds}} throws error whenever the batchIds list was empty. In the context of {{FileStreamSource.getBatch}} (where verify is called) and FileStreamSourceLog (subclass of HDFSMetadata), this is usually okay because, in a streaming query with one file stream, the batchIds can never be empty:

A batch is planned only when the FileStreamSourceLog has seen new offset (that is, there are new data files).
So FileStreamSource.getBatch will be called on X to Y where X will always be > Y. This calls internally {{HDFSMetadata.verifyBatchIds (X+1, Y)}} with X+1-Y ids.
For example, {{FileStreamSource.getBatch(4, 5)}} will call {{verify(batchIds = Seq(5), start = 5, end = 5)}}. However, the invariant of X > Y is not true when there are two file stream sources, as a batch may be planned even when only one of the file streams has data. So one of the file stream may not have data, which can call {{FileStreamSource.getBatch(X, X) -> verify(batchIds = Seq.empty, start = X+1, end = X) -> failure}}.

Note that FileStreamSource.getBatch(X, X) gets called only when restarting a query in a batch where a file source did not have data. This is because, in normal planning of batches, MicroBatchExecution avoids calling {{FileStreamSource.getBatch(X, X)}} when offset X has not changed. However, when restarting a stream at such a batch, {{MicroBatchExecution.populateStartOffsets()}} calls {{FileStreamSource.getBatch(X, X)}} (DataSource V1 hack to initialize the source with last known offsets) thus hitting this issue.


**Solution**
The minimum solution (that can be backported) here is to skip verification when FileStreamSource.getBatch(X, X).



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