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From "Jiandan Yang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-12200) Optimize CachedDNSToSwitchMapping to avoid 100% cpu utilization
Date Thu, 27 Jul 2017 09:24:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-12200?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16102989#comment-16102989
] 

Jiandan Yang  commented on HDFS-12200:
--------------------------------------

[~brahmareddy] Please help me review it. Thanks a log. 

> Optimize CachedDNSToSwitchMapping to avoid 100% cpu utilization
> ---------------------------------------------------------------
>
>                 Key: HDFS-12200
>                 URL: https://issues.apache.org/jira/browse/HDFS-12200
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>            Reporter: Jiandan Yang 
>            Assignee: Jiandan Yang 
>         Attachments: cpu_ utilization.png, HDFS-12200-001.patch, HDFS-12200-002.patch,
HDFS-12200-003.patch, nn_thread_num.png
>
>
> 1. Background :
> Our hadoop cluster is disaggregated storage and compute, HDFS is deployed to 600+ machines,
YARN is deployed to another machine pool.
> We found that sometimes NameNode cpu utilization rate of 90% or even 100%. The most serious
is cpu utilization rate of 100% for a long time result in writing journalNode timeout, eventually
leading to NameNode hang up. The reason is  offline tasks running in a few hundred servers
access HDFS at the same time, NameNode resolve rack of client machine, started several hundreds
to two thousand  sub-process. 
> {code:java}
> "process reaper"#10864 daemon prio=10 os_prio=0 tid=0x00007fe270a31800 nid=0x38d93 runnable
[0x00007fcdc36fc000]
>    java.lang.Thread.State: RUNNABLE
>         at java.lang.UNIXProcess.waitForProcessExit(Native Method)
>         at java.lang.UNIXProcess.lambda$initStreams$4(UNIXProcess.java:301)
>         at java.lang.UNIXProcess$$Lambda$7/1447689627.run(Unknown Source)
>         at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1147)
>         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:622)
>         at java.lang.Thread.run(Thread.java:834
> {code}
> Our configuration as follows:
> {code:java}
> net.topology.node.switch.mapping.impl = ScriptBasedMapping, 
> net.topology.script.file.name = 'a python script'
> {code}
> 2. Optimization
> In order to solve these two problems, we have optimized the CachedDNSToSwitchMapping
> (1) Added the DataNode IP list  to the file of  dfs.hosts configured. when NameNode starts
it  preloads DataNode rack information to the cache, get a batch of racks of hosts when running
script once (the corresponding configuration is net.topology.script.number,the default value
of 100)
> (2) Step (1) has ensured that the cache has all the DataNodes’ rack,  so if the cache
did not hit, then the host must be a client machine, then directly return /default-rack,
> (3) Each time you add new DataNodes you need to add the new DataNodes’ IP address to
the file specified by dfs.hosts, and then run command of bin/hdfs dfsadmin -refreshNodes,
it will put the newly added DataNodes’ rack into cache
> (4) Add new configuration items dfs.namenode.topology.resolve-non-cache-host, the value
is false to open the above function, and the value is true to turn off the above functions,
default value is true to keep compatibility



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