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From "Marcus Eriksson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7272) Add "Major" Compaction to LCS
Date Fri, 06 Feb 2015 06:42:36 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7272?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14308704#comment-14308704
] 

Marcus Eriksson commented on CASSANDRA-7272:
--------------------------------------------

The data in that big sstable generated from a major compaction would "never" be compacted.
It would contain old data and would most likely block us from dropping tombstones in the regular
minor compactions. This does not help 100% but it is atleast better.

> Add "Major" Compaction to LCS 
> ------------------------------
>
>                 Key: CASSANDRA-7272
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7272
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: T Jake Luciani
>            Assignee: Marcus Eriksson
>            Priority: Minor
>              Labels: compaction
>             Fix For: 3.0
>
>
> LCS has a number of minor issues (maybe major depending on your perspective).
> LCS is primarily used for wide rows so for instance when you repair data in LCS you end
up with a copy of an entire repaired row in L0.  Over time if you repair you end up with multiple
copies of a row in L0 - L5.  This can make predicting disk usage confusing.  
> Another issue is cleaning up tombstoned data.  If a tombstone lives in level 1 and data
for the cell lives in level 5 the data will not be reclaimed from disk until the tombstone
reaches level 5.
> I propose we add a "major" compaction for LCS that forces consolidation of data to level
5 to address these.



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