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From "Aaron T. Myers (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3070) HDFS balancer doesn't ensure that hdfs-site.xml is loaded
Date Sat, 31 Mar 2012 16:18:26 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3070?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13243208#comment-13243208

Aaron T. Myers commented on HDFS-3070:

bq. I remember, in our Jenkins it will spawn separate JVM for each test class. no?

True, but if that test class starts a MiniDFSCluster to run the balancer against, then the
test won't detect any problem with the balancer, since the MiniDFSCluster will cause HdfsConfiguration
to be class-loaded.

Uma, if I'm misunderstanding what you're proposing, perhaps you could post some code to illustrate
how this would work? If you do, I'll be sure to review it promptly.

In the mean time, I'm going to go ahead and commit this patch since everyone seems to agree
that this will fix the bug.
> HDFS balancer doesn't ensure that hdfs-site.xml is loaded
> ---------------------------------------------------------
>                 Key: HDFS-3070
>                 URL: https://issues.apache.org/jira/browse/HDFS-3070
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: balancer
>    Affects Versions: 2.0.0
>            Reporter: Stephen Chu
>            Assignee: Aaron T. Myers
>         Attachments: HDFS-3070.patch, unbalanced_nodes.png, unbalanced_nodes_inservice.png
> I TeraGenerated data into DataNodes styx01 and styx02. Looking at the web UI, both have
over 3% disk usage.
> Attached is a screenshot of the Live Nodes web UI.
> On styx01, I run the _hdfs balancer_ command with threshold 1% and don't see the blocks
being balanced across all 4 datanodes (all blocks on styx01 and styx02 stay put).
> HA is currently enabled.
> [schu@styx01 ~]$ hdfs haadmin -getServiceState nn1
> active
> [schu@styx01 ~]$ hdfs balancer -threshold 1
> 12/03/08 10:10:32 INFO balancer.Balancer: Using a threshold of 1.0
> 12/03/08 10:10:32 INFO balancer.Balancer: namenodes = []
> 12/03/08 10:10:32 INFO balancer.Balancer: p         = Balancer.Parameters[BalancingPolicy.Node,
> Time Stamp               Iteration#  Bytes Already Moved  Bytes Left To Move  Bytes Being
> Balancing took 95.0 milliseconds
> [schu@styx01 ~]$ 
> I believe with a threshold of 1% the balancer should trigger blocks being moved across
DataNodes, right? I am curious about the "namenode = []" from the above output.
> [schu@styx01 ~]$ hadoop version
> Hadoop 0.24.0-SNAPSHOT
> Subversion git://styx01.sf.cloudera.com/home/schu/hadoop-common/hadoop-common-project/hadoop-common
-r f6a577d697bbcd04ffbc568167c97b79479ff319
> Compiled by schu on Thu Mar  8 15:32:50 PST 2012
> From source with checksum ec971a6e7316f7fbf471b617905856b8
> From http://hadoop.apache.org/hdfs/docs/r0.21.0/api/org/apache/hadoop/hdfs/server/balancer/Balancer.html:
> The threshold parameter is a fraction in the range of (0%, 100%) with a default value
of 10%. The threshold sets a target for whether the cluster is balanced. A cluster is balanced
if for each datanode, the utilization of the node (ratio of used space at the node to total
capacity of the node) differs from the utilization of the (ratio of used space in the cluster
to total capacity of the cluster) by no more than the threshold value. The smaller the threshold,
the more balanced a cluster will become. It takes more time to run the balancer for small
threshold values. Also for a very small threshold the cluster may not be able to reach the
balanced state when applications write and delete files concurrently.

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