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From "nkeywal (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3703) Decrease the datanode failure detection time
Date Mon, 10 Sep 2012 18:50:08 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3703?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13452303#comment-13452303
] 

nkeywal commented on HDFS-3703:
-------------------------------

Hi,

For the DFSInputStream#readBlockLength, I got it I think: the LocatedBlocks class contains
two sub structures:
- a list of LocatedBlocks
- a lastLocatedBlocks for the blocks in construction

Today, the patch does the reorder only for the first structure, it should be done for the
second one as well. I tested (by hacking, not directly in HDFS) in HBase, I didn't get any
network error in my test.

To me, it's a part of the read path, so it should be included in this patch.


I'm ok to create another JIRA for the write path, I will do it.


Thank you all for your work!

Nicolas


                
> Decrease the datanode failure detection time
> --------------------------------------------
>
>                 Key: HDFS-3703
>                 URL: https://issues.apache.org/jira/browse/HDFS-3703
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: data-node, name-node
>    Affects Versions: 1.0.3, 2.0.0-alpha
>            Reporter: nkeywal
>            Assignee: Suresh Srinivas
>         Attachments: HDFS-3703-branch2.patch, HDFS-3703.patch, HDFS-3703-trunk-read-only.patch,
HDFS-3703-trunk-with-write.patch
>
>
> By default, if a box dies, the datanode will be marked as dead by the namenode after
10:30 minutes. In the meantime, this datanode will still be proposed  by the nanenode to write
blocks or to read replicas. It happens as well if the datanode crashes: there is no shutdown
hooks to tell the nanemode we're not there anymore.
> It especially an issue with HBase. HBase regionserver timeout for production is often
30s. So with these configs, when a box dies HBase starts to recover after 30s and, while 10
minutes, the namenode will consider the blocks on the same box as available. Beyond the write
errors, this will trigger a lot of missed reads:
> - during the recovery, HBase needs to read the blocks used on the dead box (the ones
in the 'HBase Write-Ahead-Log')
> - after the recovery, reading these data blocks (the 'HBase region') will fail 33% of
the time with the default number of replica, slowering the data access, especially when the
errors are socket timeout (i.e. around 60s most of the time). 
> Globally, it would be ideal if HDFS settings could be under HBase settings. 
> As a side note, HBase relies on ZooKeeper to detect regionservers issues.

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