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https://issues.apache.org/jira/browse/CASSANDRA-4929?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sylvain Lebresne updated CASSANDRA-4929:
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Attachment: 4929.txt
> Deal with broken ALTER DROP support in CQL3
> -------------------------------------------
>
> Key: CASSANDRA-4929
> URL: https://issues.apache.org/jira/browse/CASSANDRA-4929
> Project: Cassandra
> Issue Type: Bug
> Affects Versions: 1.2.0 beta 1
> Reporter: Sylvain Lebresne
> Assignee: Sylvain Lebresne
> Priority: Minor
> Fix For: 1.2.0 rc1
>
> Attachments: 4929.txt
>
>
> Currently, {{ALTER DROP}} only remove the metadata for the column, making it
> unavailable, but don't reclaim the data. This is unintuive and CASSANDRA-3919
> is opened to fix it. However, that later issue won't make it for 1.2, and I
> think we should be very careful into shipping 1.2 with the current behavior
> because 1) it's unintuitive and 2) as unintuitive as it is, we don't want
> people to start relying on that behavior. So I thing we should do one of:
> * remove support for {{ALTER DROP}} until CASSANDRA-3919 reintroduce it.
> After all, there is no real performance impact in keeping a colum that you
> don't use and if you really really want to get rid of the metadata, you still
> have the workaround of trashing the schema and recreating it without that
> column (obviously not user friendly, but at least it's vaguely possible).
> * add a specific syntax for the current behavior of {{ALTER DROP}}, one that
> clearly imply that the data is not deleted, if we consider that this behavior
> can be sometimes useful (that is, even after CASSANDRA-3919 is resolved). One
> such syntax could one of (not sure which one I prefer):
> {noformat}
> ALTER TABLE foo DROP my_column SCHEMA ONLY
> ALTER TABLE foo DROP my_column KEEP DATA
> {noformat}
> I have a slight preference for solution 2, but honestly because it will it
> easier to drop a column you've just added but maybe mispelled the name until
> CASSANDRA-3919. Once CASSANDRA-3919 is in, I'm not sure this will be so
> useful anymore.
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