Mailing-List: contact core-dev-help@hadoop.apache.org; run by ezmlm
Precedence: bulk
Reply-To: core-dev@hadoop.apache.org
Message-ID: <1643210905.1214938965078.JavaMail.jira@brutus>
Date: Tue, 1 Jul 2008 12:02:45 -0700 (PDT)
From: "Tsz Wo (Nicholas), SZE (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-3673) Deadlock in Datanode RPC servers
In-Reply-To: <871530531.1214872244961.JavaMail.jira@brutus>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit


    [ https://issues.apache.org/jira/browse/HADOOP-3673?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12609685#action_12609685 ] 

Tsz Wo (Nicholas), SZE commented on HADOOP-3673:
------------------------------------------------

> A third option would be to let the client talk to the datanodes before calling "recoverBlock()", so that we don't invoke an RPC from another RPC.

It might not be possible since recoverBlock() calls both getBlockMetaDataInfo(...) and updateBlock(...).

> 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
>
> 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.