[jira] [Created] (HDFS-16890) Add period state refresh to keep router state near active namenode's

["Simbarashe Dzinamarira (Jira)" <ji...@apache.org>]

Simbarashe Dzinamarira created HDFS-16890:
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             Summary: Add period state refresh to keep router state near active namenode's
                 Key: HDFS-16890
                 URL: https://issues.apache.org/jira/browse/HDFS-16890
             Project: Hadoop HDFS
          Issue Type: Task
            Reporter: Simbarashe Dzinamarira


When using the ObserverReadProxyProvider, clients can set 

*dfs.client.failover.observer.auto-msync-period...* to periodically get the Active namenode's state. When using routers without the ObserverReadProxyProvider, this periodic update is lost.

In a busy cluster, the Router constantly gets updated with the active namenode's state when
 # There is a write operation.
 # There is an operation (read/write) from a new clients.

However, in the scenario when there are no new clients and no write operations, the state kept in the router can lag behind the active's. The router does update its state with responses from the Observer, but the observer may be lagging behind too.

We should have a periodic refresh in the router to serve a similar role as *dfs.client.failover.observer.auto-msync-period*



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