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From "Chris Nauroth (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-8432) Introduce a minimum compatible layout version to allow downgrade in more rolling upgrade use cases.
Date Wed, 03 Jun 2015 21:30:40 GMT

     [ https://issues.apache.org/jira/browse/HDFS-8432?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Chris Nauroth updated HDFS-8432:
--------------------------------
    Attachment: HDFS-8432.002.patch

[~arpitagarwal] pointed out to me that I had set some wrong values for the minimum compatible
layout versions.  {{TRUNCATE}} was added in Apache Hadoop 2.7.0 as layout version -61.  We
need to set its minimum compatible layout version to -61.  (Setting it to itself means it
is not downgradeable to any prior versions.)  By extension, we also need to set {{APPEND_NEW_BLOCK}}
and {{QUOTA_BY_STORAGE_TYPE}} to minimum compatible layout version -61.  Those features also
shipped in Apache Hadoop 2.7.0, so it wouldn't make sense to claim those features are downgradeable
to any pre-truncate version.

Thank you for the review, Arpit.  Here is patch v002.  I also addressed the Jenkins feedback
from the last run.

> Introduce a minimum compatible layout version to allow downgrade in more rolling upgrade
use cases.
> ---------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-8432
>                 URL: https://issues.apache.org/jira/browse/HDFS-8432
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode, rolling upgrades
>            Reporter: Chris Nauroth
>            Assignee: Chris Nauroth
>         Attachments: HDFS-8432-HDFS-Downgrade-Extended-Support.pdf, HDFS-8432.001.patch,
HDFS-8432.002.patch
>
>
> Maintain the prior layout version during the upgrade window and reject attempts to use
new features until after the upgrade has been finalized.  This guarantees that the prior software
version can read the fsimage and edit logs if the administrator decides to downgrade.  This
will make downgrade usable for the majority of NameNode layout version changes, which just
involve introduction of new edit log operations.



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