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From "Pavel Yaskevich (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-1902) Migrate cached pages during compaction
Date Tue, 29 Mar 2011 14:37:06 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1902?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13012506#comment-13012506
] 

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

NativeMappedSegment if used to give us a better control over memory-mapped region of the file,
especially for skipping page cache using (madvice(DONT_NEED) and utilizing a mapping by native
way - munmap and doing page cache migration. NormalMappedSegment is used in cases when we
don't have a page size (JNA is not installed or not on Linux). I have added those methods
because it's not possible to clean page cache from the region of the MBB, also using NativeMappedSegment
we don't need to duplicate buffers on slice calls.

> 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: 0.7.5, 0.8
>
>         Attachments: 0001-CASSANDRA-1902-cache-migration-impl-with-config-option.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
>
>   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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