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https://issues.apache.org/jira/browse/HDFS-4721?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13641075#comment-13641075
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Tsz Wo (Nicholas), SZE commented on HDFS-4721:
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> ... lease recovery can occur and the lease be reassigned to someone else
> while the block has not been recovered which is, its totally possible for
> lease to be recovered without the block being recovered ...
If the block is still being recovered, the new lease holder should not be able
write to the file.
> Basically, I see that call "recoverLease" - lease is recovered and block
> recovery enqueued for bad replica (without this patch). Call recoverLease
> again and it says lease recovery was successful even though the block was
> never recovered. ...
Do the mean the block is corrupted?
recoverLease return true only if the file is closed. If not, it is a bug.
> 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-trunk.patch,
> 4721-trunk-v2.patch, 4721-v2.patch, 4721-v3.patch, 4721-v4.patch,
> 4721-v5.patch, 4721-v6.patch, 4721-v7.patch, 4721-v8.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
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