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From "Harsh J (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7501) TransactionsSinceLastCheckpoint can be negative on SBNs
Date Fri, 20 Feb 2015 16:07:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7501?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14329098#comment-14329098
] 

Harsh J commented on HDFS-7501:
-------------------------------

Hey [~ggop], can you switch the method to simply make use of FSImage.getLastAppliedOrWrittenTxId(…)
method? That should work just fine for both ANN and SBN modes, as it appears to track both
written mode edits and tailed mode edits.

The test can be modified to be a test of "> 0" as opposed to "= 0" as we previously targeted.

> 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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