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https://issues.apache.org/jira/browse/HDFS-7501?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14383596#comment-14383596
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Akira AJISAKA commented on HDFS-7501:
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Looks good to me, +1. Thanks [~qwertymaniac] and [~ggop].
> TransactionsSinceLastCheckpoint can be negative on SBNs
> -------------------------------------------------------
>
> Key: HDFS-7501
> URL: https://issues.apache.org/jira/browse/HDFS-7501
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Affects Versions: 2.5.0
> Reporter: Harsh J
> Assignee: Gautam Gopalakrishnan
> Priority: Trivial
> Attachments: HDFS-7501-2.patch, HDFS-7501-3.patch, HDFS-7501.patch
>
>
> The metric TransactionsSinceLastCheckpoint is derived as FSEditLog.txid minus
> NNStorage.mostRecentCheckpointTxId.
> In Standby mode, the former does not increment beyond the loaded or
> last-when-active value, but the latter does change due to checkpoints done
> regularly in this mode. Thereby, the SBN will eventually end up showing
> negative values for TransactionsSinceLastCheckpoint.
> This is not an issue as the metric only makes sense to be monitored on the
> Active NameNode, but we should perhaps just show the value 0 by detecting if
> the NN is in SBN form, as allowing a negative number is confusing to view
> within a chart that tracks it.
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