gresockj opened a new pull request #5025:
URL: https://github.com/apache/nifi/pull/5025
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#### Description of PR
Previously, when a cluster with at least 3 nodes offloaded the first node
(the one targeted by a Single Node load balanced queue), only the offloaded
node updated its list of partitions in the SocketLoadBalancedFlowFileQueue's
partitionQueue. If the offloaded node reconnected, its queue would list the
second node first, but all other nodes (including the second node) would still
have the first node listed first. Therefore, an infinite loop resulted where
the first node would be balancing its flowfiles to the second node, and the
second node would balance all of its flowfiles to the first node. The result
was that this particular queue would ignore backpressure and the following
processor would never be reached, at the same time.
All that said, this fix does the following to resolve the issue:
# Causes all non-offloading nodes to remove the offloading node from their
partitionQueues in SocketLoadBalancedFlowFileQueue, whenever the OFFLOADING
node state change is detected. This allows all other nodes to be in sync with
the first node's partitionQueue.
# Causes all non-offloading nodes (of which the previously offloaded node
will now be one) to add back a node to the partition queue upon CONNECTED node
state change. This allows the offloaded node to regain its place as the "first
node" in Single Node load balancing.
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