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From "Sylvain Lebresne (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3442) TTL histogram for sstable metadata
Date Wed, 02 Nov 2011 08:50:32 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3442?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13142006#comment-13142006
] 

Sylvain Lebresne commented on CASSANDRA-3442:
---------------------------------------------

I think the idea has merits.
We have to keep in mind that unless the expired data is also gcable, this would only transform
expiring columns to tombstones, so for those that have very small columns (~4 bytes) this
would be useless. I would also maybe bump that 20% up to be sure we don't rewrite too ofen
sstables that are good candidate for compaction anyway. But on principle this is a good idea
I believe. 
                
> TTL histogram for sstable metadata
> ----------------------------------
>
>                 Key: CASSANDRA-3442
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3442
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Sylvain Lebresne
>            Priority: Minor
>              Labels: compaction
>
> Under size-tiered compaction, you can generate large sstables that compact infrequently.
 With expiring columns mixed in, we could waste a lot of space in this situation.
> If we kept a TTL EstimatedHistogram in the sstable metadata, we could do a single-sstable
compaction aginst sstables with over 20% (?) expired data.

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