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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11742) Improve balancer usability after HDFS-8818
Date Sat, 10 Jun 2017 17:40:18 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11742?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16045628#comment-16045628
] 

Konstantin Shvachko commented on HDFS-11742:
--------------------------------------------

Hi [~kihwal], thanks for the data. Shows your point well.

I have a 2600-node cluster, where we've been running Balancer pretty actively. This was initially
based on 2.6, but now pretty close to branch-2.7, and with  HDFS-8818 applied. Here is the
graph, thanks [~xkrogen] for generating it:

!https://issues.apache.org/jira/secure/attachment/12872444/replaceBlockNumOps-8w.jpg!

The maximum number of transfers is 50 - close to yours. We do not allow the Balancer to run
"full speed" to allow room for normal workload on the cluster. So I am not completely sure
that HDFS-8818 is the only thing to blame for the slowness you described. I did not run branch-2.8
Balancer, but I plan to test on branch-2.7 in the very near future.

Also looked at your patch. Sounds like a reasonable change to me. But may be we want to understand
more closely at the root cause of the behavior before we commit?

> Improve balancer usability after HDFS-8818
> ------------------------------------------
>
>                 Key: HDFS-11742
>                 URL: https://issues.apache.org/jira/browse/HDFS-11742
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Kihwal Lee
>            Assignee: Kihwal Lee
>            Priority: Blocker
>              Labels: release-blocker
>         Attachments: balancer2.8.png, balancer_fix.png, HDFS-11742.branch-2.8.patch,
HDFS-11742.branch-2.patch, HDFS-11742.trunk.patch, HDFS-11742.v2.trunk.patch, replaceBlockNumOps-8w.jpg,
replaceBlockNumOps-8w.png
>
>
> We ran 2.8 balancer with HDFS-8818 on a 280-node and a 2,400-node cluster. In both cases,
it would hang forever after two iterations. The two iterations were also moving things at
a significantly lower rate. The hang itself is fixed by HDFS-11377, but the design limitation
remains, so the balancer throughput ends up actually lower.
> Instead of reverting HDFS-8188 as originally suggested, I am making a small change to
make it less error prone and more usable.



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