[jira] [Updated] (HDFS-8432) Introduce a minimum compatible layout version to allow downgrade in more rolling upgrade use cases.

["Chris Nauroth (JIRA)" <ji...@apache.org>]

     [ 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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