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From "Harsh J (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-7501) TransactionsSinceLastCheckpoint can be negative on SBNs
Date Tue, 24 Mar 2015 19:11:53 GMT

     [ https://issues.apache.org/jira/browse/HDFS-7501?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Harsh J updated HDFS-7501:
--------------------------
    Attachment: HDFS-7501-3.patch

I went ahead and modified the patch with the suggested change above, and also added some indent
cleanup + comments to the great test written there (aside of the fix to the test as required
for the new changes).

New test fails as expected without the fix, and passes all 3 criterion with the fix.

Attaching and marking as Patch Available to run full module tests via jenkins.

> 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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