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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-774) Datanodes fails to heartbeat when a directory with a large number of blocks is deleted
Date Mon, 04 Dec 2006 18:39:22 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-774?page=comments#action_12455384 ] 
Raghu Angadi commented on HADOOP-774:

I think (1) is simpler, from namenode point of view.

One modification for (1) is that, Datanode should first delete the mapping inline and queue
the physical file deletion on a separate thread.  This is required so that Datanode does not
send the already invalidated blocks in in its next heartbeat.

Of course,  datanode should not create one thread for each RPC call. It could delete them
inline if the number is small (say < 20), otherwise queue them up to be deleted by a thread
(It will create one if one does not exist). The thread exits if there are no files to be deleted.

> Datanodes fails to heartbeat when a directory with a large number of blocks is deleted
> --------------------------------------------------------------------------------------
>                 Key: HADOOP-774
>                 URL: http://issues.apache.org/jira/browse/HADOOP-774
>             Project: Hadoop
>          Issue Type: Bug
>          Components: dfs
>            Reporter: dhruba borthakur
>         Assigned To: dhruba borthakur
> If a user removes a few files that are huge, it causes the namenode to send BlockInvalidate
command to the relevant Datanodes. The Datanode process the blockInvalidate command as part
of its heartbeat thread. If the number of blocks to be invalidated is huge, the datanode takes
a long time to process it. This causes the datanode to not send new heartbeats to the namenode.
The namenode declares the datanode as dead!
> 1. One option is to process the blockInvalidate as a separate thread from the heartbeat
thread in the Datanode. 
> 2. Another option would be to constrain the namenode to send a max (e.g. 500) blocks
per blockInvalidate message.

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