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https://issues.apache.org/jira/browse/CASSANDRA-3929?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13210358#comment-13210358
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Sylvain Lebresne commented on CASSANDRA-3929:
---------------------------------------------

Agreed, it's hard to do efficiently. What is easy to do is to write a 
compaction strategy (or have a strategy option) that only keeps the N first 
columns on each compaction. Of course, that doesn't guarantee that you will 
only get the N most recent columns but in practice that would fairly 
efficiently get rid of the excess data, which I believe is mostly what people 
care about. Basically it would really just be "we'll discard everything we know 
is out of the N first columns". I suspect that in practice that may be the good 
trade-off, but given it's not perfect I've always though that it probably make 
more sense as an externally contributed compaction strategy.
                
> Support row size limits
> -----------------------
>
>                 Key: CASSANDRA-3929
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3929
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Jonathan Ellis
>            Priority: Minor
>              Labels: ponies
>
> We currently support expiring columns by time-to-live; we've also had 
> requests for keeping the most recent N columns in a row.

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