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From "Sylvain Lebresne (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3919) Dropping a column should do more than just remove the definition
Date Thu, 05 Apr 2012 07:19:31 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3919?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13247066#comment-13247066
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Sylvain Lebresne commented on CASSANDRA-3919:
---------------------------------------------

Actually I think there is a small problem, which is 'what if someone drop a column, then add
it back later'? I guess there is a few options there:
# don't allow to add back a dropped column ever
# have a way to know when the column have been fully purged from the data, and only allow
to re-add the column then (but we'd have to check that *all* node have purged it first).
# assume that the column timestamp is a real timestamp. Then in the dropped_columns set we
could keep the timestamp of when the column was drop, and if it is added back, during read
we would return the column only if the timestamp > dropped_timestamp.

My preference goes to 3 as this feels actually easier to get right than 2 and is much less
limiting than 1. Note that even with 3, we could still add a way to know when the column has
been fully purged so that we remove it to the dropped_colums set (but that can be left to
a following ticket as it would really just be an optimisation).
                
> Dropping a column should do more than just remove the definition
> ----------------------------------------------------------------
>
>                 Key: CASSANDRA-3919
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3919
>             Project: Cassandra
>          Issue Type: Sub-task
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Sylvain Lebresne
>              Labels: compaction, cql
>             Fix For: 1.1.1
>
>
> Dropping a column should:
> - immediately make it unavailable for {{SELECT}}, including {{SELECT *}}
> - eventually (i.e., post-compaction) reclaim the space formerly used by that column

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