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