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From Colin McCabe <cmcc...@alumni.cmu.edu>
Subject Re: Heartbeat interval and timeout: why 3 secs and 10 min?
Date Wed, 13 Mar 2013 18:08:48 GMT
My understanding is that the 10 minute timeout helps to avoid replication
storms, especially during startup.

You might be interested in HDFS-3703, which adds a "stale" state which
datanodes are placed into after 30 seconds of missing heartbeats.  (This is
an optional feature controlled by dfs.namenode.check.stale.datanode )

best,
Colin


On Tue, Mar 12, 2013 at 5:29 PM, André Oriani <aoriani@gmail.com> wrote:

> No take on this one?
>
> In Zookeeper the heartbeats happen on every third of the timeout.  If I am
> not mistaken, recomended timeout is  more than 2 minutes to avoid false
> positives.
>
> But I still cannot see the relationship on HDFS between heartbeat interval
> and timeout. Okay 10 minutes seems to be a conservative value to avoid
> false positives in  a big cluster. But that means 200 hearbeats. Heartbeats
> on HDFS are not only used for liveness detection but also to send
> information about free space and load and to receive commands from
> NameNode. So they are also essential for block placement decisions and for
> ensuring the replication levels. Would that then be reason why heartbeats
> are so frequent? A lot can happen to a DataNode in just three seconds?
>
>
> Thanks,
> André Oriani
>
>
>
> On Thu, Mar 7, 2013 at 10:37 PM, André Oriani <aoriani@gmail.com> wrote:
>
> > Hi,
> >
> > Is there any particular reason why the default heartbeat interval is 3
> > seconds and the timeout is 10 minutes? Everywhere I looked (code, Google,
> > ..) only mentions  the values but no clue on why those values were
> chosen.
> >
> >
> > Thanks in advance,
> > André Oriani
> >
>

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