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https://issues.apache.org/jira/browse/HDFS-1172?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14907769#comment-14907769
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Masatake Iwasaki commented on HDFS-1172:
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bq. Looks like the rebased patches only put not-yet-received replicas into the
pending replication queue, but BlockManager#checkReplication has not been
updated accordingly
I think it is better to leave {{BlockManager#checkReplication}} as is here.
Though it may add block having pending replicas to {{neededReplications}}, the
replication will not be scheduled as far as the replica is in
{{pendingReplications}} because {{BlockManager#hasEnoughEffectiveReplicas}}
takes it into account.
{{BlockManager#isNeededReplication}} is used in other places. Keeping the
condition for updating {{neededReplications}} consistent makes the code clear
and will avoid potential bugs.
bq. 2. makes sure that blocks except for the last block in a file
under-construction get replicated when under-replicated; This will allow a
decommissioning datanode to finish decommissioning even it has replicas in
files under construction.
{{TestReplication#testReplicationWhileUnderConstruction}} checks this is
satisfied.
> Blocks in newly completed files are considered under-replicated too quickly
> ---------------------------------------------------------------------------
>
> Key: HDFS-1172
> URL: https://issues.apache.org/jira/browse/HDFS-1172
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 0.21.0
> Reporter: Todd Lipcon
> Attachments: HDFS-1172-150907.patch, HDFS-1172.008.patch,
> HDFS-1172.009.patch, HDFS-1172.patch, hdfs-1172.txt, hdfs-1172.txt,
> replicateBlocksFUC.patch, replicateBlocksFUC1.patch, replicateBlocksFUC1.patch
>
>
> I've seen this for a long time, and imagine it's a known issue, but couldn't
> find an existing JIRA. It often happens that we see the NN schedule
> replication on the last block of files very quickly after they're completed,
> before the other DNs in the pipeline have a chance to report the new block.
> This results in a lot of extra replication work on the cluster, as we
> replicate the block and then end up with multiple excess replicas which are
> very quickly deleted.
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