[jira] Commented: (CASSANDRA-1902) Migrate cached pages during compaction

["T Jake Luciani (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-1902?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12995861#comment-12995861 ] 

T Jake Luciani commented on CASSANDRA-1902:
-------------------------------------------

Attached new version with a configuration to enable/disable(default) this and CASSANDRA-1470 if you are going to test you need to set enable_page_cache_migration: true in cassandra.yaml

> 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: 0.7.2
>
>         Attachments: 0001-CASSANDRA-1902-cache-migration-impl-with-config-option.txt
>
>   Original Estimate: 32h
>          Time Spent: 24h
>  Remaining Estimate: 8h
>
> 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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