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From "Sameer Paranjpye (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-563) DFS client should try to re-new lease if it gets a lease expiration exception when it adds a block to a file
Date Thu, 28 Sep 2006 20:24:51 GMT
     [ http://issues.apache.org/jira/browse/HADOOP-563?page=all ]

Sameer Paranjpye updated HADOOP-563:
------------------------------------

    Component/s: dfs
    Description: 
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.

 

  was:

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.

 


> 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
>
> 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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