[jira] [Created] (APEXMALHAR-2037) Reconciled jdbc output operator with ability to spool to disk

["Ashwin Chandra Putta (JIRA)" <ji...@apache.org>]

Ashwin Chandra Putta created APEXMALHAR-2037:
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             Summary: Reconciled jdbc output operator with ability to spool to disk
                 Key: APEXMALHAR-2037
                 URL: https://issues.apache.org/jira/browse/APEXMALHAR-2037
             Project: Apache Apex Malhar
          Issue Type: New Feature
            Reporter: Ashwin Chandra Putta
            Assignee: Ashwin Chandra Putta


There are many use cases in which we are writing tuples to external system using jdbc etc. There are instances when the external system might be slow and down for some time. In those cases, the current implementation of jdbc output operators fail and restart until the external system is up again. Meanwhile, the DAG is slowed down by this operator. To deal with such scenarios, we can write the output in a reconciled fashion where the reconciler thread is writing at the pace of external system. We should also provide an ability to spool the data to disk when the external system is down or the output operators queue is full.

Here are the proposed features for the output operator.

1. Write to external system in a separate reconciler thread.
2. Queue the tuples in memory for reconciler thread to consume. 
3. Spool the incoming tuples to hdfs using a WAL when the queue size is reached.
4. Read from WAL and write to queue as queue is being consumed.
5. When external system is able to consumer as fast as incoming throughput, WAL is not written. The queue will just buffer the tuples before writing to external system.



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