[jira] [Updated] (HADOOP-15486) Add a config option to make NetworkTopology#netLock fair

["Arpit Agarwal (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-15486?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Arpit Agarwal updated HADOOP-15486:
-----------------------------------
    Summary: Add a config option to make NetworkTopology#netLock fair  (was: Make NetworkTopology#netLock fair)

> Add a config option to 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
>            Priority: Major
>
> 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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