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Date: Tue, 27 Nov 2012 00:00:59 +0000 (UTC)
From: "Hudson (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <527520096.25348.1353974459999.JavaMail.jiratomcat@arcas>
In-Reply-To: <2008030447.22608.1353931018097.JavaMail.jiratomcat@arcas>
Subject: [jira] [Commented] (HBASE-7217) Documentation: Update section
 11.5.1 to recommend that hbase.regionserver.checksum.verify is set
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    [ https://issues.apache.org/jira/browse/HBASE-7217?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13504250#comment-13504250 ] 

Hudson commented on HBASE-7217:
-------------------------------

Integrated in HBase-TRUNK-on-Hadoop-2.0.0 #274 (See [https://builds.apache.org/job/HBase-TRUNK-on-Hadoop-2.0.0/274/])
    HBASE-7217 Documentation: Update section 11.5.1 to recommend that hbase.regionserver.checksum.verify is set (Revision 1413793)

     Result = FAILURE
stack : 
Files : 
* /hbase/trunk/src/docbkx/performance.xml

                
> Documentation: Update section 11.5.1 to recommend that hbase.regionserver.checksum.verify is set
> ------------------------------------------------------------------------------------------------
>
>                 Key: HBASE-7217
>                 URL: https://issues.apache.org/jira/browse/HBASE-7217
>             Project: HBase
>          Issue Type: Improvement
>          Components: documentation
>    Affects Versions: 0.94.2
>            Reporter: Neil Ferguson
>            Priority: Minor
>             Fix For: 0.96.0
>
>         Attachments: 7217.txt
>
>
> When short-circuit reads are enabled (dfs.client.read.shortcircuit = true), reading with checksums enabled (dfs.client.read.shortcircuit.skip.checksum = false) follows a completely different, and much slower, path to reading with checksums disabled (BlockReaderLocal uses something called a "slow buffer", which is, unsurprisingly, slow). My tests show that this path is actually slower than having short-circuit reads disabled.
> Therefore, I think section 11.5.1 of the HBase documentation should recommend that hbase.regionserver.checksum.verify be set to true when using short-circuit reads. I'd suggest the following:
> "For optimal performance when short-circuit reads are enabled, it is recommended that HDFS checksums are disabled. To maintain data integrity with HDFS checksums disabled, HBase can be configured to write its own checksums into its datablocks and verify against these. See Section 11.4.9. "hbase.regionserver.checksum.verify".

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