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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-5342) ancestors are not cleared in SSTableMetadata after compactions are done and old SSTables are removed
Date Sat, 06 Jul 2013 01:11:52 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5342?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13701217#comment-13701217
] 

Jonathan Ellis commented on CASSANDRA-5342:
-------------------------------------------

LGTM.

Nit: since we only ever use either the metadata, or the anscestors, it may be cleaner to split
deserializeAncestors into a separate method.  OTOH that might make it easier to make mistakes
in compatibility.  I'm fine either way.
                
> ancestors are not cleared in SSTableMetadata after compactions are done and old SSTables
are removed
> ----------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-5342
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-5342
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 1.1.3
>            Reporter: Wei Zhu
>            Assignee: Marcus Eriksson
>             Fix For: 1.2.7
>
>         Attachments: 0001-CASSANDRA-5342-wip.patch, 0001-CASSANDRA-5342-wip-v2.patch,
Screen Shot 2013-03-13 at 12.05.08 PM.png
>
>
> We are using LCS and have total of 38000 SSTables for one CF. During LCS, there could
be over a thousand SSTable involved. All those SSTable IDs are stored in ancestors field of
SSTableMetatdata for the new table. In our case, it consumes more than 1G of heap memory for
those field. Put it in perspective, the ancestors consume 2 - 3 times more memory than bloomfilter
(fp = 0.1 by default) in LCS. 
> We should remove those ancestors from SSTableMetadata after the compaction is finished
and the old SSTable is removed. It  might be a big deal for Sized Compaction since there are
small number of SSTable involved. But it consumes a lot of memory for LCS. 
> At least, we shouldn't load those ancestors to the memory during startup if the files
are removed. 
> I would love to contribute and provide patch. Please let me know how to start. 

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