Xiaoqiao He created HDFS-17090:
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Summary: Decommission will be stuck for long time when restart
because overlapped process Register and BlockReport.
Key: HDFS-17090
URL: https://issues.apache.org/jira/browse/HDFS-17090
Project: Hadoop HDFS
Issue Type: Bug
Components: namenode
Reporter: Xiaoqiao He
Assignee: Xiaoqiao He
I met one corner case recently, which decommission DataNode impact performance
of NameNode. After dig carefully, I have reproduced this case.
a. Add some DataNodes to exclude and prepare to decommission this Datanodes.
b. Execute bin/hdfs dfsadmin -refresh (This is optional step).
c. Restart NameNode for upgrade or other reason before complete to decommission.
d. All DataNodes will be trigger to register and FBR.
e. Considering that the load of NameNode will be very high, especially 8040
CallQueue will be full for a long time because RPC flood about
register/heartbeat/FBR from DataNodes.
f. For one decommission in-progress node, it will not complete to decommission
until next FBR even all replicas of this node has been processed, because the
request order register-heartbeat-(blockreport, register), and the second
register could be one retry RPC request from DataNode (No more log information
from DataNode to confirm), and for (blockreport, register), NameNode could
process one storage then process register then process remaining storages in
order.
g. Because the second register RPC, the related DataNodes will be marked
unhealthy by BlockManager#isNodeHealthyForDecommissionOrMaintenance. So
decommission will be stuck for long time until next FBR. Thus NameNode need to
scan this DataNode at every round to check if could complete which hold the
global write lock and impact performance of NameNode.
To improve it, I think we could filter the repeated register RPC request at
startup progress. Not think carefully if it will involve other risks when
filter register directly. Welcome anymore discussions.
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