operatorremove.md

Flow of operator being removed from the plan

An operator can request shutdown by throwing ShutdownException from any of operator lifecycle method. StramChild terminate the operator thread also does some finalization if required such as calling endWindow or taking a checkpoint for exactly once processing. From now on the operator stats sent by the container does not contain any stats for this operator.

On master during heartbeat processing processHeartbeat, master checks for any missmatch between expected number of operators in a container and actually reported operators by the heartbeat, master takes following actions

• For extra operator reported, send undeploy request in heartbeat response.
• For missing operator, remove physical operator from the physical plan.

StreamingContianerManager shutdownOperators variabel maintains list of operators needs to be shutdown. The operator can be safely removed if

• operator window id is less than or equal to the committedWindowId.

• All downstream operators have windowId equal to the operator being removed.

  • processHeartbeat
    • processOperatorDeployStatus If operator state changes from ACTIVE to SHUTDOWN add it to the shutdownOperators map. shutDownOperators is a map from windowId to list of operators which have shutdown in this window.

  In processEvent after statshandlers are called shutdownOperators map is processed and these operators are removed from physical plan.

important functions to study

• removeTerminatedPartition - remove the physical partition also downstream operator if their input is empty after removing current operator.

• removePTOperator : remove unifiers, remove inputs from downstream operators, remove from upstream operator. remove from operator grouping.

• removePartition : remove parallel partitions recursively, update pamapping and call remotePTOperator at end.