huangtengfei created SPARK-24351:
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Summary: offsetLog/commitLog purge thresholdBatchId should be
computed with current committed epoch but not currentBatchId in CP mode
Key: SPARK-24351
URL: https://issues.apache.org/jira/browse/SPARK-24351
Project: Spark
Issue Type: Bug
Components: Structured Streaming
Affects Versions: 2.3.0
Reporter: huangtengfei
In structured streaming, there is a conf spark.sql.streaming.minBatchesToRetain
which is set to specify 'The minimum number of batches that must be retained
and made recoverable' as described in
[SQLConf](https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala#L802).
In continuous processing, the metadata purge is triggered when an epoch is
committed in
[ContinuousExecution](https://github.com/apache/spark/blob/master/sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/continuous/ContinuousExecution.scala#L306).
Since currentBatchId increases independently in cp mode, the current committed
epoch may be far behind currentBatchId if some task hangs for some time. It is
not safe to discard the metadata with thresholdBatchId computed based on
currentBatchId because we may clean all the metadata in the checkpoint
directory.
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