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From "Daryn Sharp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3224) Bug in check for DN re-registration with different storage ID
Date Tue, 09 Oct 2012 17:20:04 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3224?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13472558#comment-13472558
] 

Daryn Sharp commented on HDFS-3224:
-----------------------------------

Suresh, it's that {{Hosts2NodesMap}} is internally decided on how it will key the node in
the map.  Now the caller assumes that it knows how the node is keyed when fetching the node.
 Two possible approaches to decouple them are: 1) the caller specifies the map key for the
node, and again specifies the same key when fetching a node.  Or the node is passed to the
fetch so {{Hosts2NodesMap}} can extract the same key as it did when adding the node to the
map.

It's kind of the same situation where the {{TokenCache}} assumed it knew how the fs token
would be keyed in the {{Credentials}}.  When the assumption went out of sync in some cases,
it caused extra tokens to be fetched.  In this case it would confuse the node manager as to
whether the node is new or a replacement.
                
> Bug in check for DN re-registration with different storage ID
> -------------------------------------------------------------
>
>                 Key: HDFS-3224
>                 URL: https://issues.apache.org/jira/browse/HDFS-3224
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Eli Collins
>            Assignee: Jason Lowe
>            Priority: Minor
>         Attachments: HDFS-3224.patch, HDFS-3224.patch
>
>
> DatanodeManager#registerDatanode checks the host to node map using an IP:port key, however
the map is keyed on IP, so this check will always fail. It's performing the check to determine
if a DN with the same IP and storage ID has already registered, and if so to remove this DN
from the map and indicate that eg it's no longer hosting these blocks. This bug has been here
forever.

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