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From "Marcus Eriksson (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, 25 May 2013 14:27:20 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-5342?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13667085#comment-13667085
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Marcus Eriksson commented on CASSANDRA-5342:
--------------------------------------------

have not really followed #5151 so these is my quite out-of-context thoughts:

as far as i can see they are only read during startup, maybe we could not keep a reference
to them after flushing the metadata, and then reading them on startup only to be able to remove
the compaction leftovers? and then clear them out the same way we mutate sstable level?

i could have a go
                
> 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
>             Fix For: 1.2.6
>
>         Attachments: 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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