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Date: Fri, 24 Dec 2010 16:06:45 -0500 (EST)
From: "Jonathan Ellis (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
Subject: [jira] Updated: (CASSANDRA-1902) Migrate cached pages during
 compaction
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     [ https://issues.apache.org/jira/browse/CASSANDRA-1902?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jonathan Ellis updated CASSANDRA-1902:
--------------------------------------

    Fix Version/s: 0.7.1

> Migrate cached pages during compaction 
> ---------------------------------------
>
>                 Key: CASSANDRA-1902
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1902
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 0.7.1
>            Reporter: T Jake Luciani
>            Assignee: T Jake Luciani
>             Fix For: 0.7.1
>
>
> Post CASSANDRA-1470 there is an opportunity to migrate cached pages from a pre-compacted CF during the compaction process.  
> First, add a method to MmappedSegmentFile: long[] pagesInPageCache() that uses the posix mincore() function to detect the offsets of pages for this file currently in page cache.
> Then add getActiveKeys() which uses underlying pagesInPageCache() to get the keys actually in the page cache.
> use getActiveKeys() to detect which SSTables being compacted are in the os cache and make sure the subsequent pages in the new compacted SSTable are kept in the page cache for these keys. This will minimize the impact of compacting a "hot" SSTable.
> A simpler yet similar approach is described here: http://insights.oetiker.ch/linux/fadvise/

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