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https://issues.apache.org/jira/browse/AMBARI-19527?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Nate Cole reopened AMBARI-19527:
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> Downgrade executes <pre-upgrade> section if <pre-downgrade> is not defined
> --------------------------------------------------------------------------
>
> Key: AMBARI-19527
> URL: https://issues.apache.org/jira/browse/AMBARI-19527
> Project: Ambari
> Issue Type: Bug
> Components: ambari-server
> Reporter: Nate Cole
> Assignee: Nate Cole
> Priority: Critical
> Fix For: 2.5.0
>
> Attachments: AMBARI-19527_1.patch
>
>
> When creating the initial upgrade packs, an effort was made to make them as
> least-verbose as possible. In that, we assumed that all tasks that occurred
> during an Upgrade would also occur on a Downgrade. That assumption led to
> some sneaky bugs that are difficult to troubleshoot.
> The real fix is to make the XSD enforce "sibling" elements, such that when
> PRE-UPGRADE tasks are defined, you can enforce that a PRE-DOWNGRADE element
> exist. Unfortunately, the JDK (even 1.8) doesn't support that version of XSD
> in JAXB.
> The interim solution was to use the afterUnmarshal secret sauce to validate
> that the elements exist. Allow a pre-downgrade or post-downgrade element to
> indicate that it can reuse the (pre-post)upgrade element definitions.
> Many of the changes here are in upgrade packs to add the new required
> elements, and the unit test that parses all upgrade packs passes.
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