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https://issues.apache.org/jira/browse/HDFS-12914?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16844178#comment-16844178
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Santosh Marella commented on HDFS-12914:
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{quote} Santosh Marella how many DNs do you have? According to the limited
logs, I think it is caused by following case. A high cpu load of SNN delayed
the processing of full block report.{quote}
DNs are in the order of hundreds. You are right that a high cpu load on SNN has
delayed processing a FBR from a DN that was issued a lease. The SNN started
processing the reports, but the lease expired after it processed 3 out of 12
reports.
> Block report leases cause missing blocks until next report
> ----------------------------------------------------------
>
> Key: HDFS-12914
> URL: https://issues.apache.org/jira/browse/HDFS-12914
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 2.8.0
> Reporter: Daryn Sharp
> Priority: Critical
>
> {{BlockReportLeaseManager#checkLease}} will reject FBRs from DNs for
> conditions such as "unknown datanode", "not in pending set", "lease has
> expired", wrong lease id, etc. Lease rejection does not throw an exception.
> It returns false which bubbles up to {{NameNodeRpcServer#blockReport}} and
> interpreted as {{noStaleStorages}}.
> A re-registering node whose FBR is rejected from an invalid lease becomes
> active with _no blocks_. A replication storm ensues possibly causing DNs to
> temporarily go dead (HDFS-12645), leading to more FBR lease rejections on
> re-registration. The cluster will have many "missing blocks" until the DNs
> next FBR is sent and/or forced.
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