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From "Philip Luppens (JIRA)" <j...@apache.org>
Subject [jira] [Created] (FLINK-8484) Kinesis consumer re-reads
Date Mon, 22 Jan 2018 17:16:00 GMT
Philip Luppens created FLINK-8484:

             Summary: Kinesis consumer re-reads 
                 Key: FLINK-8484
                 URL: https://issues.apache.org/jira/browse/FLINK-8484
             Project: Flink
          Issue Type: Bug
          Components: Kinesis Connector
    Affects Versions: 1.3.2
            Reporter: Philip Luppens

We’re using the connector to subscribe to streams varying from 1 to a 100 shards, and used
the kinesis-scaling-utils to dynamically scale the Kinesis stream up and down during peak
times. What we’ve noticed is that, while we were having closed shards, any Flink job restart
with check- or save-point would result in shards being re-read from the event horizon, duplicating
our events.


We started checking the checkpoint state, and found that the shards were stored correctly
with the proper sequence number (including for closed shards), but that upon restarts, the
older closed shards would be read from the event horizon, as if their restored state would
be ignored.


In the end, we believe that we found the problem: in the FlinkKinesisConsumer’s run() method,
we’re trying to find the shard returned from the KinesisDataFetcher against the shards’
metadata from the restoration point, but we do this via a containsKey() call, which means
we’ll use the StreamShardMetadata’s equals() method. However, this checks for all properties,
including the endingSequenceNumber, which might have changed between the restored state’s
checkpoint and our data fetch, thus failing the equality check, failing the containsKey()
check, and resulting in the shard being re-read from the event horizon, even though it was
present in the restored state.


We’ve created a workaround where we only check for the shardId and stream name to restore
the state of the shards we’ve already seen, and this seems to work correctly. 

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