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https://issues.apache.org/jira/browse/HDFS-4183?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13496766#comment-13496766
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Kihwal Lee commented on HDFS-4183:
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bq. Could we simply jitter the lease expiration time? The 1 hour limit isn't
anything precise which a user would depend on. I could see adding a 10% jitter
to smooth out the expirations over time.
If it is a short burst, jitter will scatter the burst. But if it's a long
burst, this won't help much. In some cases, over 40K block recoveries were
still outstanding after an hour and caused the leases held by namenode during
recovery to expire, resulting in yet another storm of block recoveries.
bq. Any idea why it's so slow aside from the logging? Do we have a silly bug
where we are logSyncing while holding the lock or something?
I couldn't find anything in commitBlockSynchronization(), but releasing lease
and initiating block recover may be the source of problem.
internalReleaseLease() : this is called from the lease monitor with the write
lock held
-> reassignLease()
-> logReassignLease() : reacquires the write lock and logSync() happens.
So it looks like logSync() is done holding the write lock during lease release
& scheduling block recovery.
We should probably hold off this jira and fix that first.
> Throttle block recovery
> -----------------------
>
> Key: HDFS-4183
> URL: https://issues.apache.org/jira/browse/HDFS-4183
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: name-node
> Affects Versions: 0.23.4, 2.0.2-alpha
> Reporter: Kihwal Lee
> Assignee: Kihwal Lee
> Priority: Critical
>
> When a large number of files are abandoned without closing, a storm of lease
> expiration follows in about an hour (lease hard limit). For the last block of
> each file, block recovery is initiated and when the datanode is done, it
> calls commitBlockSynchronization() is called against namenode. A burst of
> these calls can slow down namenode considerably. We need to throttle block
> recovery and/or speed up the rate at which commitBlockSynchronization() is
> served.
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