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From "Harsh J (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3475) Make the replication monitor multipliers configurable
Date Thu, 21 Jun 2012 21:55:44 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3475?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13398912#comment-13398912
] 

Harsh J commented on HDFS-3475:
-------------------------------

Btw I finally played around with the block repl multiplier on a local cluster and I could
notice increase in usage when a DN went down and the blocks began moving about, with a higher
multiplier value. The logs grepped and counted too showed higher "asking DN to replicate"
count per DN heartbeat at NN.

This should be cautiously increased though, cause even if your network is awesome, your disks
cumulatively need to keep up with it anyway. And too much of payload per DN command transfer-back
is bad as well. This is why the defaults, I've stuck them as-is and added warnings in documented
props.
                
> Make the replication monitor multipliers configurable
> -----------------------------------------------------
>
>                 Key: HDFS-3475
>                 URL: https://issues.apache.org/jira/browse/HDFS-3475
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>    Affects Versions: 2.0.0-alpha
>            Reporter: Harsh J
>            Assignee: Harsh J
>            Priority: Trivial
>         Attachments: HDFS-3475.patch
>
>
> BlockManager currently hardcodes the following two constants:
> {code}
> private static final int INVALIDATE_WORK_PCT_PER_ITERATION = 32;
> private static final int REPLICATION_WORK_MULTIPLIER_PER_ITERATION = 2;
> {code}
> These are used to throttle/limit the amount of deletion and replication-to-other-DN work
done per heartbeat interval of a live DN.
> Not many have had reasons to want these changed so far but there have been a few requests
I've faced over the past year from a variety of clusters I've helped maintain. I think with
the improvements in disks and network thats already started to be rolled out in production
environments out there, changing these may start making sense to some.
> Lets at least make it advanced-configurable with proper docs that warn adequately, with
the defaults being what they are today. With hardcodes, it comes down to a recompile for admins,
which is not something they may like.
> Please let me know your thoughts.

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