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From "Pavel Yaskevich (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-1902) Migrate cached pages during compaction
Date Sun, 10 Apr 2011 22:27:06 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1902?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13018167#comment-13018167
] 

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

I have been thinking about change in SSTableScanner to use SSTableReader.dfile instead of
BRAF which can potentially give us the following benefits: 

a). don't need to skip a cache because we will be operating on memory mappings
b). better performance (not copying data between kernel and user buffers as effect gained
from using memory mapped segments, avoiding time operating on the kernel mode (+ time for
switching context and read-ahead pressure) which BRAF involves)
c). less impact on the live-reads
d). less garbage will be created
e). less file descriptors opened

What do you think? (of course, this should be done in the separate task)

> 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, CASSANDRA-1902-v7.patch, CASSANDRA-1902-v8.patch, CASSANDRA-1902-v9-trunk-with-jmx.patch,
CASSANDRA-1902-v9-trunk.patch, CASSANDRA-1902-v9.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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