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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2736) HA: support separate SBN and 2NN?
Date Fri, 30 Dec 2011 22:24:30 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2736?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13177791#comment-13177791
] 

Todd Lipcon commented on HDFS-2736:
-----------------------------------

bq. if we fail over to the SBN does it continue to checkpoint?

If the only active NN comes back, it will start in standby mode and then do checkpoints against
the other one. It's only if the former active remains dead for some time that we might have
a problem.

bq. If not the log grows unbounded until the old primary comes back, if so does that create
performance problems since the primary wasn't previously checkpointing?
Certainly the first startup after a long outage will be slower, since it has to replay a lot
of transactions. But it's not any different than what happens today if the 2NN goes down for
some length of time.

Given that people currently run successfully with only a single 2NN, I don't think this is
particularly high priority. Do you disagree?
                
> HA: support separate SBN and 2NN?
> ---------------------------------
>
>                 Key: HDFS-2736
>                 URL: https://issues.apache.org/jira/browse/HDFS-2736
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: ha
>    Affects Versions: HA branch (HDFS-1623)
>            Reporter: Eli Collins
>
> HDFS-2291 adds support for making the SBN capable of checkpointing, seems like we may
also need to support the 2NN checkpointing as well. Eg if we fail over to the SBN does it
continue to checkpoint? If not the log grows unbounded until the old primary comes back, if
so does that create performance problems since the primary wasn't previously checkpointing?

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