[HDFS-11334] [SPS]: NN switch and rescheduling movements can lead to have more than one coordinator for same file blocks

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: HDFS-10285
• Fix Version/s: HDFS-10285, 3.2.0
• Component/s: datanode, namenode
• Hadoop Flags: Reviewed
• Assignee: Rakesh Radhakrishnan
• Reporter: Uma Maheswara Rao G
• Created: 11/Jan/17 22:10
• Updated: 13/Aug/18 05:40
• Resolved: 18/Apr/17 22:28

Description

I am summarizing the scenarios here what Rakesh and me discussed offline:
Here we need to handle couple of cases:

1. NN switch - it will freshly start scheduling for all files.
   At this time, old co-ordinators may continue movement work and send results back. This could confuse NN SPS that which result is right one.
   NEED TO HANDLE
2. DN disconnected for heartbeat expiry - If DN disconnected for long time(more than heartbeat expiry), NN will remove this nodes. After SPS Monitor time out, it may retry for files which were scheduled to that DN, by finding new co-ordinator. But if it reconnects back after NN reschedules, it may lead to get different results from deferent co-ordinators.
   NEED TO HANDLE
3. NN Restart- Should be same as point 1
4. DN disconnect - here When DN disconnected simply and reconnected immediately (before heartbeat expiry), there should not any issues
   NEED NOT HANDLE, but can think of more scenarios if any thing missing
5. DN Restart- If DN restarted, DN can not send any results as it will loose everything. After NN SPS Monitor timeout, it will retry.
   NEED NOT HANDLE, but can think of more scenarios if any thing missing