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From "Jing Zhao (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6353) Handle checkpoint failure more gracefully
Date Fri, 16 May 2014 17:34:15 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14000026#comment-14000026
] 

Jing Zhao commented on HDFS-6353:
---------------------------------

Thanks for the comments, [~kihwal]. I think we already have LastCheckpointTime, MostRecentCheckpointTxId,
and LastAppliedOrWrittenTxId exposed through jmx. Ambari already uses these for monitoring
and alerting.

> Handle checkpoint failure more gracefully
> -----------------------------------------
>
>                 Key: HDFS-6353
>                 URL: https://issues.apache.org/jira/browse/HDFS-6353
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: namenode
>            Reporter: Suresh Srinivas
>            Assignee: Jing Zhao
>
> One of the failure patterns I have seen is, in some rare circumstances, due to some inconsistency
the secondary or standby fails to consume editlog. The only solution when this happens is
to save the namespace at the current active namenode. But sometimes when this happens, unsuspecting
admin might end up restarting the namenode, requiring more complicated solution to the problem
(such as ignore editlog record that cannot be consumed etc.).
> How about adding the following functionality:
> When checkpointer (standby or secondary) fails to consume editlog, based on a configurable
flag (on/off) to let the active namenode know about this failure. Active namenode can enters
safemode and saves namespace. When  in this type of safemode, namenode UI also shows information
about checkpoint failure and that it is saving namespace. Once the namespace is saved, namenode
can come out of safemode.
> This means service unavailability (even in HA cluster). But it might be worth it to avoid
long startup times or need for other manual fixes. Thoughts?



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