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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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