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From "Lei (Eddy) Xu (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-12044) Mismatch between BlockManager#maxReplicatioStreams and ErasureCodingWorker.stripedReconstructionPool pool size causes slow and burst recovery.
Date Tue, 27 Jun 2017 00:38:00 GMT
Lei (Eddy) Xu created HDFS-12044:
------------------------------------

             Summary: Mismatch between BlockManager#maxReplicatioStreams and ErasureCodingWorker.stripedReconstructionPool
pool size causes slow and burst recovery. 
                 Key: HDFS-12044
                 URL: https://issues.apache.org/jira/browse/HDFS-12044
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: erasure-coding
    Affects Versions: 3.0.0-alpha3
            Reporter: Lei (Eddy) Xu


{{ErasureCodingWorker#stripedReconstructionPool}} is with {{corePoolSize=2}} and {{maxPoolSize=8}}
as default. And it rejects more tasks if the queue is full.

When {{BlockManager#maxReplicationStream}} is larger than {{ErasureCodingWorker#stripedReconstructionPool#corePoolSize/maxPoolSize}},
for example, {{maxReplicationStream=20}} and {{corePoolSize=2 , maxPoolSize=8}}.  Meanwhile,
NN sends up to {{maxTransfer}} reconstruction tasks to DN for each heartbeat, and it is calculated
in {{FSNamesystem}}:

{code}
final int maxTransfer = blockManager.getMaxReplicationStreams() - xmitsInProgress;
{code}

However, at any giving time, {{{ErasureCodingWorker#stripedReconstructionPool}} takes 2 {{xmitInProcess}}.
So for each heartbeat in 3s, NN will send about {{20-2 = 18}} reconstruction tasks to the
DN, and DN throw away most of them if there were 8 tasks in the queue already. So NN needs
to take longer to re-consider these blocks were under-replicated to schedule new tasks.






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