Commits on Mar 27, 2020

1. Abort incomplete pipelines upon reconnect …

   Elasticache severs the connection immediately after it returns a
   READONLY error.  This can sometimes leave queued up pipelined commands
   in an inconsistent state when the connection is reestablished. For
   example, if a pipeline has 6 commands and the second one generates a
   READONLY error, Elasticache will only return results for the first two
   before severing the connection. Upon reconnect, the pipeline still
   thinks it has 6 commands to send but the commandQueue has only 4. This
   fix will detect any pipeline command sets that only had a partial
   response before connection loss, and abort them.
   
   This Elasticache behavior also affects transactions. If reconnectOnError
   returns 2, some transaction fragments may end up in the offlineQueue.
   This fix will check the offlineQueue for any such transaction fragments
   and abort them, so that we don't send mismatched multi/exec to redis
   upon reconnection.
   
   - Introduced piplineIndex property on pipelined commands to allow for later
   cleanup
   - Added a routine to event_handler that aborts any pipelined commands inside
   commandQueue and offlineQueue that were interrupted in the middle of the
   pipeline
   - Added a routine to event_handler that removes any transaction
   fragments from the offline queue
   - Introduced inTransaction property on commands to simplify pipeline logic
   - Added a flags param to mock_server to allow the Elasticache disconnect
   behavior to be simulated
   - Added a reconnect_on_error test case for transactions
   - Added some test cases testing for correct handling of this unique elasticache
   behavior
   - Added unit tests to validate inTransaction and pipelineIndex setting
   
   Fixes redis#965

   

   alavers committed Mar 27, 2020
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