[
https://issues.apache.org/jira/browse/HADOOP-3673?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12609934#action_12609934
]
Sameer Paranjpye commented on HADOOP-3673:
------------------------------------------
Is there any reason that the primary datanode alone can do recovery? If not,
then this becomes classic Dining Philosophers. The client always invokes
recoverBlock() on the lowest (by some sort order) datanode in it's pipeline.
This 'recovery primary' in turn invokes other nodes in the pipeline in the same
sort order. We'd still have to remove the datanodes RPC to itself.
> Deadlock in Datanode RPC servers
> --------------------------------
>
> Key: HADOOP-3673
> URL: https://issues.apache.org/jira/browse/HADOOP-3673
> Project: Hadoop Core
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.18.0
> Reporter: dhruba borthakur
> Priority: Blocker
> Fix For: 0.18.0
>
>
> There is a deadlock scenario in the way Lease Recovery is triggered using the
> Datanode RPC server via HADOOP-3283.
> Each Datanode has dfs.datanode.handler.count handler threads (default of 3).
> These handler threads are used to support the generation-stamp-dance protocol
> as described in HADOOP-1700.
> Let me try to explain the scenario with an example. Suppose, a cluster has
> two datanodes. Also, let's assume that dfs.datanode.handler.count is set to
> 1. Suppose that there are two clients, each writing to a separate file with a
> replication factor of 2. Let's assume that both clients encounter an IO error
> and triggers the generation-stamp-dance protocol. The first client may invoke
> recoverBlock on the first datanode while the second client may invoke
> recoverBlock on the second datanode. Now, each of the datanode will try to
> make a getBlockMetaDataInfo() to the other datanode. But since each datanode
> has only 1 server handler threads, both threads will block for eternity.
> Deadlock!
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
