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  1. Flink
  2. FLINK-8487

State loss after multiple restart attempts

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      Description

      A user reported this issue on the user@f.a.o mailing list and analyzed the situation.

      Scenario:

      • A program that reads from Kafka and computes counts in a keyed 15 minute tumbling window. StateBackend is RocksDB and checkpointing is enabled.
      keyBy(0)
              .timeWindow(Time.of(window_size, TimeUnit.MINUTES))
              .allowedLateness(Time.of(late_by, TimeUnit.SECONDS))
              .reduce(new ReduceFunction(), new WindowFunction())
      
      • At some point HDFS went into a safe mode due to NameNode issues
      • The following exception was thrown
      org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.ipc.StandbyException): Operation category WRITE is not supported in state standby. Visit https://s.apache.org/sbnn-error
          ..................
      
          at org.apache.flink.runtime.fs.hdfs.HadoopFileSystem.mkdirs(HadoopFileSystem.java:453)
              at org.apache.flink.core.fs.SafetyNetWrapperFileSystem.mkdirs(SafetyNetWrapperFileSystem.java:111)
              at org.apache.flink.runtime.state.filesystem.FsCheckpointStreamFactory.createBasePath(FsCheckpointStreamFactory.java:132)
      
      • The pipeline came back after a few restarts and checkpoint failures, after the HDFS issues were resolved.
      • It was evident that operator state was lost. Either it was the Kafka consumer that kept on advancing it's offset between a start and the next checkpoint failure (a minute's worth) or the the operator that had partial aggregates was lost.

      The user did some in-depth analysis (see mail thread) and might have (according to Aljoscha Krettek) identified the problem.

      Stefan Richter, can you have a look at this issue and check if it is relevant?

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            • Assignee:
              aljoscha Aljoscha Krettek
              Reporter:
              fhueske Fabian Hueske
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              • Created:
                Updated:
                Resolved: