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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-140) Prevent linux from caching write ahead log files
Date Wed, 09 May 2012 16:49:49 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-140?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13271581#comment-13271581
] 

Todd Lipcon commented on ACCUMULO-140:
--------------------------------------

HDFS uses fadvise(DONT_NEED) in addition to sync_file_range to trigger early writeback. sync_file_range
has a flag to enqueue for writeback without forcing a true fsync, which is nicer on the rest
of the system (eg doesn't force a journal fsync like a normal fsync() does). Check out BlockReceiver.java
in trunk DFS.
                
> Prevent linux from caching write ahead log files
> ------------------------------------------------
>
>                 Key: ACCUMULO-140
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-140
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: logger
>            Reporter: Keith Turner
>            Assignee: Eric Newton
>             Fix For: 1.5.0
>
>
> While at ApacheCon I attended a talk about Cassandra.  The developer mentioned using
posix_fadvise to prevent linux from storing edit/write ahead log data in the page cache. 
This sounds great.  Accumulo can do this for its write ahead logs.
> Using posix_fadvise was also mentioned for compactions, this is something Accumulo can
not do because its compactions read and write to hdfs.

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