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From "Sebastian Toader (JIRA)" <>
Subject [jira] [Created] (AMBARI-17248) Reduce the idle time before first command from next stage is executed on a host
Date Wed, 15 Jun 2016 08:43:09 GMT
Sebastian Toader created AMBARI-17248:

             Summary: Reduce the idle time before first command from next stage is executed
on a host
                 Key: AMBARI-17248
             Project: Ambari
          Issue Type: Improvement
          Components: ambari-agent, ambari-server
            Reporter: Sebastian Toader
            Assignee: Sebastian Toader
             Fix For: 2.2-next, 2.5.0

Commands to be executed by ambari-agents are being sent down by the server in the response
message to agent heartbeat messages. 
The server processes the received heartbeat, it checks if there are next commands scheduled
to be executed by ambari-agent and adds those to the heartbeat response for the ambari-agent.
The server organises the commands that can be executed in parallel into stages. Ambari server
ensures that only the commands of a single stage is scheduled to be executed by the agent
and starts scheduling the commands of the next stage only after all commands of current stage
has finished successfully.
The processing of command status received with the heartbeat message happens asynchronously
to heartbeat response in HeartBeatProcessor and ActionScheduler creation thus when the heartbeat
response is created the commands for the next stage are not scheduled yet. This means that
the next commands will be sent to agent only with the next heartbeat.
Agents currently sends a heartbeat to the server on command a completion or at a timeout =
interval which is ~10 seconds if there are no commands to be executed.
This means that when the server receives a heartbeat triggered by the completion of the last
command from the current stage the server will send the commands for the next stage only 10
seconds later when the next heartbeat is received. This leads to agents spending considerable
amount of time idle when there are multiple stages to be executed.

Agents should heartbeat at a higher rate while there are still pending stages to be executed.

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