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Date: Thu, 31 Mar 2011 18:34:06 +0000 (UTC)
From: "Pavel Yaskevich (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (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:comment-tabpanel&focusedCommentId=13014128#comment-13014128 ] 

Pavel Yaskevich commented on CASSANDRA-1902:
--------------------------------------------

I have an idea of how to avoid mmap at all at SSTableIdentityIterator by using SSTableReader.dfile which is already mmaped in segments, it should lower i/o pressure during compaction with migration ON.

> 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: Pavel Yaskevich
>             Fix For: 0.7.5, 0.8
>
>         Attachments: 0001-CASSANDRA-1902-cache-migration-impl-with-config-option.txt, 1902-BufferedSegmentedFile-logandsleep.txt, 1902-formatted.txt, 1902-per-column-migration-rebase2.txt, 1902-per-column-migration.txt, CASSANDRA-1902-v3.patch, CASSANDRA-1902-v4.patch, CASSANDRA-1902-v5.patch, CASSANDRA-1902-v6.patch
>
>   Original Estimate: 32h
>          Time Spent: 56h
>  Remaining Estimate: 0h
>
> Post CASSANDRA-1470 there is an opportunity to migrate cached pages from a pre-compacted CF during the compaction process.  This is now important since CASSANDRA-1470 caches effectively nothing.  
> For example an active CF being compacted hurts reads since nothing is cached in the new SSTable. 
> The purpose of this ticket then is to make sure SOME data is cached from active CFs. This can be done my monitoring which Old SSTables are in the page cache and caching active rows in the New SStable.
> A simpler yet similar approach is described here: http://insights.oetiker.ch/linux/fadvise/

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