Harsh J created HDFS-7501:
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Summary: 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
Priority: Trivial
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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