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https://issues.apache.org/jira/browse/HDFS-1172?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14933772#comment-14933772
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Jing Zhao commented on HDFS-1172:
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bq. BlockManager#hasEnoughEffectiveReplicas added by HDFS-8938 takes pending
replicas into account. numCurrentReplica in BlockManager#addStoredBlock was
fixed to take pending replicas into account by HDFS-8623.
These two jiras are mainly doing only code refactoring. The logic has been
there for a while.
bq. 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.
The question is, if we expect later replication monitor to remove the block
from {{neededReplication}}, why do we add it in the first place? Also if a
block's effective replica number (including pending replica number) is >= than
its replication factor, the block should not be in {{neededReplication}}. This
is more consistent with the current logic.
> 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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