Nanda kumar created HADOOP-15486:
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Summary: Make NetworkTopology#netLock fair
Key: HADOOP-15486
URL: https://issues.apache.org/jira/browse/HADOOP-15486
Project: Hadoop Common
Issue Type: Improvement
Components: net
Reporter: Nanda kumar
Assignee: Nanda kumar
Whenever a datanode is restarted, the registration call after the restart
received by NameNode lands in {{NetworkTopology#add}} via
{{DatanodeManager#registerDatanode}} requires write lock on
{{NetworkTopology#netLock}}. This registration thread is getting starved by
flood of {{FSNamesystem.getAdditionalDatanode}} calls, which are triggered by
clients those who were writing to the restarted datanode.
The registration call which is waiting for write lock on
{{NetworkTopology#netLock}} is holding write lock on {{FSNamesystem#fsLock}},
causing all the other RPC calls which require the lock on
{{FSNamesystem#fsLock}} wait.
We can make {{NetworkTopology#netLock}} lock fair so that the registration
thread will not starve.
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