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From "Gautam Gopalakrishnan (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7501) TransactionsSinceLastCheckpoint can be negative on SBNs
Date Mon, 12 Jan 2015 07:49:34 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7501?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14273288#comment-14273288
] 

Gautam Gopalakrishnan commented on HDFS-7501:
---------------------------------------------

[~daryn] any thoughts?

> 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.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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