hadoop-hdfs-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Varun Sharma (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-4721) Speed up lease/block recovery when DN fails and a block goes into recovery
Date Mon, 22 Apr 2013 23:29:18 GMT

    [ https://issues.apache.org/jira/browse/HDFS-4721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13638569#comment-13638569
] 

Varun Sharma commented on HDFS-4721:
------------------------------------

Hi Nicholas,

Thanks for taking a look...

In my v2 patch, I am sorting the datanode in BlockInfoUnderConstruction.initializeBlockRecovery()
by lastUpdate and then picking the 0-th element from the sorted list. I actually want to remember
which node was tried the first time because if a subsequent block recovery was called - we
don't want to have the same DN do the recovery again. So, basically choose the node which
gave the latest heartbeat and was not the node which was issued the previous recovery.

So, you think we should unconditionally remove stale nodes (currently 30 second stale interval)
- I can surely attach a patch which has that.




                
> Speed up lease/block recovery when DN fails and a block goes into recovery
> --------------------------------------------------------------------------
>
>                 Key: HDFS-4721
>                 URL: https://issues.apache.org/jira/browse/HDFS-4721
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 2.0.3-alpha
>            Reporter: Varun Sharma
>             Fix For: 2.0.4-alpha
>
>         Attachments: 4721-hadoop2.patch, 4721-v2.patch
>
>
> This was observed while doing HBase WAL recovery. HBase uses append to write to its write
ahead log. So initially the pipeline is setup as
> DN1 --> DN2 --> DN3
> This WAL needs to be read when DN1 fails since it houses the HBase regionserver for the
WAL.
> HBase first recovers the lease on the WAL file. During recovery, we choose DN1 as the
primary DN to do the recovery even though DN1 has failed and is not heartbeating any more.
> Avoiding the stale DN1 would speed up recovery and reduce hbase MTTR. There are two options.
> a) Ride on HDFS 3703 and if stale node detection is turned on, we do not choose stale
datanodes (typically not heart beated for 20-30 seconds) as primary DN(s)
> b) We sort the replicas in order of last heart beat and always pick the ones which gave
the most recent heart beat
> Going to the dead datanode increases lease + block recovery since the block goes into
UNDER_RECOVERY state even though no one is recovering it actively. Please let me know if this
makes sense. If yes, whether we should move forward with a) or b).
> Thanks

--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira

Mime
View raw message