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