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From "Aaron T. Myers (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2983) Relax the build version check to permit rolling upgrades within a release
Date Fri, 06 Apr 2012 02:24:23 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2983?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13247975#comment-13247975
] 

Aaron T. Myers commented on HDFS-2983:
--------------------------------------

bq. I think we should upgrade NN first. Suppose we upgrade from X to Y as in your example.
Then, upgrade can be done by (1) adding Y to conf for DN's conf, (2) upgrading NN to Y and
(3) rolling upgrade DNs to Y.

What about the case (as mentioned in [this comment|https://issues.apache.org/jira/browse/HADOOP-8209?focusedCommentId=13238562&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13238562])
where a change is only scoped to the DN, and thus we'd like to do a rolling restart of DNs
without ever bouncing the NN? I don't think your proposal allows for that.

Also, I think that the steps you describe above would have to have "perform a rolling restart
of DNs to pick up the conf change" inserted between steps 1 and 2. It seems pretty kludgy
to me to require 2 separate rolling restarts of DNs in order to perform a rolling upgrade.

bq. Comparing major/minor does not require changing conf but it also limits the rolling upgrade.
Say, v1.1 and v1.2 are actually compatible but we cannot perform the upgrade due to the version
check.

One thing I've proposed is that we could check only the major version number.

Another possibility is that we could by default check major and minor versions, but have a
config which optionally disables the minor version check, to account for the case you describe
above. How does that sound to you?
                
> Relax the build version check to permit rolling upgrades within a release
> -------------------------------------------------------------------------
>
>                 Key: HDFS-2983
>                 URL: https://issues.apache.org/jira/browse/HDFS-2983
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 2.0.0
>            Reporter: Eli Collins
>            Assignee: Aaron T. Myers
>         Attachments: HDFS-2983.patch
>
>
> Currently the version check for DN/NN communication is strict (it checks the exact svn
revision or git hash, Storage#getBuildVersion calls VersionInfo#getRevision), which prevents
rolling upgrades across any releases. Once we have the PB-base RPC in place (coming soon to
branch-23) we'll have the necessary pieces in place to loosen this restriction, though perhaps
it takes another 23 minor release or so before we're ready to commit to making the minor versions
compatible.

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