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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3677) Problems with generation stamp upgrade
Date Mon, 14 Jul 2008 17:40:32 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3677?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12613384#action_12613384

Konstantin Shvachko commented on HADOOP-3677:

The advantages of the local upgrade (or as we also call it "version upgrade") as opposed to
a distributed upgrade are that it avoids both problems stated in this jira, and also avoids
thousands of warnings during data-node startup.
In my opinion, local/version upgrade is logically correct and is not a "hack" at all, because
each data-node can complete the upgrade on its own without interacting with other data-nodes
or the name-node. The distributed upgrade should be used when such intercommunications are
required. E.g. during the crc-upgrade this was unavoidable.
The startup time will be the only disadvantage so the upgrade progress should be logged every
20-30 seconds.

> Problems with generation stamp upgrade
> --------------------------------------
>                 Key: HADOOP-3677
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3677
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.18.0
>            Reporter: Konstantin Shvachko
>            Assignee: Raghu Angadi
>            Priority: Blocker
>             Fix For: 0.18.0
> # The generation stamp upgrade renames blocks' meta-files so that the name contains the
block generation stamp as stated in HADOOP-2656.
> If a data-node has blocks that do not belong to any files and the name-node asks the
data-node to remove those blocks 
> during or before the upgrade started the data-node will remove the blocks but not the
meta-files because their names 
> are still in the old format which is not recognized by the new code. So we can end up
with a number of garbage files which
> will be hard to recognize that they are unused and the system will never remove them
> I think this should be handled by the upgrade code in the end, but may be it will be
right to fix HADOOP-3002 for the 0.18 release,
> which will avoid scheduling block removal when the name-node is in safe-mode.
> # I was not able to get the upgrade -force option to work. This option lets the name-node
proceed with a distributed upgrade even if
> the data-nodes are not able to complete their local upgrades. Did we test this feature
at all for the generation stamp upgrade?

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