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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-4971) Block report times from datanodes could converge to same time.
Date Wed, 07 Jan 2009 21:12:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-4971?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12661708#action_12661708

Tsz Wo (Nicholas), SZE commented on HADOOP-4971:

> 2) unexpected like 11:35:43, next report should be at 12:20:14

I forgot to mention that the comment is a little bit confusing: the next report is actually
around 11:35:43.  The reports after the next will be xx:20:14.

> Block report times from datanodes could converge to same time.   
> -----------------------------------------------------------------
>                 Key: HADOOP-4971
>                 URL: https://issues.apache.org/jira/browse/HADOOP-4971
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.18.0
>            Reporter: Raghu Angadi
>            Assignee: Raghu Angadi
>            Priority: Blocker
>             Fix For: 0.18.3
>         Attachments: HADOOP-4971.patch
> Datanode block reports take quite a bit of memory to process at the namenode. After the
inital report, DNs pick a random time to spread this load across at the NN. This normally
works fine. 
> Block reports are sent inside "offerService()" thread in DN. If for some reason this
thread was stuck for long time (comparable to block report interval), and same thing happens
on many DNs, all of them get back to the loop at the same time and start sending block report
then and every hour at the same time. 
> RPC server and clients in 0.18 can handle this situation fine. But since this is a memory
intensive RPC it lead to large GC delays at the NN. We don't know yet why offerService therads
seemed to be stuck, but DN should re-randomize it block report time in such cases.

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