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From "Paulo Motta (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8928) Add downgradesstables
Date Mon, 13 Jun 2016 22:12:03 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8928?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15328411#comment-15328411
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Paulo Motta commented on CASSANDRA-8928:
----------------------------------------

bq. The primary use case for downgrading sstables is to abort an upgrade. So for example,
if you're on 2.1 and want to go to 2.2 or 3.x, the upgrade plan often includes a contingency
plan to abort and revert back to the older version, including preserving data written while
in the upgraded version.

The same end result can be achieved, although with maybe a bit more of work, by backing up
sstables of the upgraded node and wiping/recreating the node in a previous version, and then
use sstableloader of the newer version to reload the data in the recreated node, which would
be easily enabled by CASSANDRA-8110. Although standalone downgrading could be nice, I'm not
sure it's really worth the effort and risk of carrying sstable writing code across multiple
versions.

bq. Would it be possible to limit the implementation of this to the core sstable data file?
We could then have an offline downgrade sstable process that would convert to the older sstable
data file and those files could be bulk loaded through that version's sstable loader into
the reverted cluster.

This is more or less the approach I'm proposing, but instead of doing an offline downgrade
only of the data file  + sstableloading afterwards, you would only need to use sstableloader
of the newer version to load newer version sstables in the reverted cluster automatically.
Wouldn't this be sufficient?

> Add downgradesstables
> ---------------------
>
>                 Key: CASSANDRA-8928
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8928
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Tools
>            Reporter: Jeremy Hanna
>            Assignee: Kaide Mu
>            Priority: Minor
>              Labels: gsoc2016, mentor
>
> As mentioned in other places such as CASSANDRA-8047 and in the wild, sometimes you need
to go back.  A downgrade sstables utility would be nice for a lot of reasons and I don't know
that supporting going back to the previous major version format would be too much code since
we already support reading the previous version.



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