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https://issues.apache.org/jira/browse/CASSANDRA-6958?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Marcus Eriksson updated CASSANDRA-6958:
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    Attachment: 0001-Use-LeveledCompactionTask-for-upgradesstables-when-L.patch

> upgradesstables does not maintain levels for existing SSTables
> --------------------------------------------------------------
>
>                 Key: CASSANDRA-6958
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-6958
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Wei Deng
>            Assignee: Marcus Eriksson
>            Priority: Critical
>             Fix For: 2.0.7
>
>         Attachments: 
> 0001-Use-LeveledCompactionTask-for-upgradesstables-when-L.patch
>
>
> Initially ran into this issue on a DSE 3.2 (C* 1.2) to DSE 4.0 (C* 2.0) 
> upgrade, and then I was able to reproduce it when testing an upgrade from C* 
> 2.0.5 to C* 2.1-beta so the problem still exists in the latest code.
> Basically after you've upgraded to the new version and run "nodetool 
> upgradesstables" on a CF/table that has been using LCS, then all of the 
> non-L0 SSTables will be changed to L0 in the upgraded SSTables. In other 
> words, they don't maintain their level and will have to go through the 
> compaction again. The problem is that if you've got thousands of non-L0 
> SSTables before the upgrade, then all of these files showing up in L0 will 
> push the system to do STCS and start to build some huge L0 tables. If a user 
> doesn't budget enough free space (for example, if they used the recommended 
> guideline and only budgeted 10% of free space because LCS is in use), then 
> this STCS in L0 effect will have them run out of space.



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