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Varun Sharma commented on HDFS-4721: ------------------------------------ I think in 99 % of cases, when we see no heart beats for 30 seconds - the datanode is dead or there is a serious issue (30 seconds is like an eternity). IMO, We should try our best bets first (recently heart beating datanodes), say upto two times and then go random/round robin - current policy is random/round robin only. As it stands today, if a data node dies and recover lease is called "only once" - the lease recovery does not happen for 1 hour. > 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, 4721-v3.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