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From "Suresh Srinivas (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 22:42:03 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3224?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13472817#comment-13472817
] 

Suresh Srinivas commented on HDFS-3224:
---------------------------------------

There are three elements in DN identity - Storage ID, host address and transfer port. When
storage ID does not change and other two elements change, it is correctly handled by the namenode.

When storage ID changes:
# Old behavior: remove any DN with matching host address (no transfer address)
## In case of single DN on the same host, correct DN is removed
## In case of multiple DNs on the same host, {color:red}a random DN is removed{color}
# Current behavior: remove any DN with matching host address + transfer address
## In case of single DN on the same host, {color:red} no DN is removed{color}
## In case of multiple DNs on the same host, {color:red}no DN is removed{color}
# Behavior with this patch: remove any DN with matching host address + transfer address
## In case of single DN on the same host, correct DN is removed
## In case of multiple DNs on the same host, correct DN is removed

When Storage ID changes with IP address and/or transfer address, we will end up having two
entries. I do not think this can be avoided.

I have seen cases in many setups where multiple DNs are being run on the same machine. Given
this, I prefer the new behavior with this patch.
                
> 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, 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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