[ http://issues.apache.org/jira/browse/HADOOP-563?page=all ]
dhruba borthakur updated HADOOP-563:
------------------------------------
Attachment: softhardlease.patch
A client's lease goes stale if it fails to renew the lease for 1 minute. After
that period, if a different client request a lease for the same file, the
resouces associated with the original lease gets reclaimed and the new
lease-request is satisfied.
A client's lease trasitions from stale to expired after a 1 hour period. At
that time all resouces associated with that lease gets reclaimed.
> DFS client should try to re-new lease if it gets a lease expiration exception
> when it adds a block to a file
> ------------------------------------------------------------------------------------------------------------
>
> Key: HADOOP-563
> URL: http://issues.apache.org/jira/browse/HADOOP-563
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Reporter: Runping Qi
> Assigned To: dhruba borthakur
> Attachments: softhardlease.patch
>
>
> In the current DFS client implementation, there is one thread responsible for
> renewing leases. If for whatever reason, that thread runs behind, the lease
> may get expired. That causes the client gets a lease expiration exception
> when writing a block. The consequence of that is very devastating: the client
> can no longer write to the file, and all the partial results up to that point
> are gone! This is especially costly for some map reduce jobs where a reducer
> may take hours or even days to sort the intermediate results before the
> actual reducing work can start.
> The problem will be solved if the flush method of DFS client can renew lease
> on demand. That is, it should try to re-new lease when it catches a lease
> expiration exception. That way, even when under heavy load and the lease
> renewing thread runs behind, the reducer task (or what ever tasks use that
> client) can preceed. That will be a huge saving in some cases (where sorting
> intermediate results take a long time to finish). We can set a limit on the
> number of retries, and may even make it configurable (or changeable at
> runtime).
> The namenode can use a different expiration time that is much higher than the
> current 1 minute lease expiration time for cleaning up the abandoned
> unclosed files.
>
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