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From Jason Rosenberg <...@squareup.com>
Subject Re: ISR shrink to 0?
Date Wed, 19 Nov 2014 06:36:37 GMT
Ok,

Makes sense.  But if the node is not actually healthy (and underwent a hard
crash) it would likely not be able to avoid an 'unclean' restart.....what
happens if unclean leader election is disabled, but there are no 'clean'
partitions available?

Jason

On Wed, Nov 19, 2014 at 12:40 AM, Jun Rao <junrao@gmail.com> wrote:

> Yes, we will preserve the last replica in ISR. This way, we know which
> replica has all committed messages and can wait for it to come back as the
> leader, if unclean leader election is disabled.
>
> Thanks,
>
> Jun
>
> On Mon, Nov 17, 2014 at 11:06 AM, Jason Rosenberg <jbr@squareup.com>
> wrote:
>
> > We have had 2 nodes in a 4 node cluster die this weekend, sadly.
> > Fortunately there was no critical data on these machines yet.
> >
> > The cluster is running 0.8.1.1, and using replication factor of 2 for 2
> > topics, each with 20 partitions.
> >
> > For sake of discussion, assume that nodes A and B are still up, and C
> and D
> > are now down.
> >
> > As expected, partitions that had one replica on a good host (A or B) and
> > one on a bad node (C or D), had their ISR shrink to just 1 node (A or B).
> >
> > Roughly 1/6 of the partitions had their 2 replicas on the 2 bad nodes, C
> > and D.  For these, I was expecting the ISR to show up as empty, and the
> > partition unavailable.
> >
> > However, that's not what I'm seeing.  When running TopicCommand
> --describe,
> > I see that the ISR still shows 1 replica, on node D (D was the second
> node
> > to go down).
> >
> > And, producers are still periodically trying to produce to node D (but
> > failing and retrying to one of the good nodes).
> >
> > So, it seems the cluster's meta data is still thinking that node D is up
> > and serving the partitions that were only replicated on C and D.
>  However,
> > for partitions that were on A and D, or B and D, D is not shown as being
> in
> > the ISR.
> >
> > Is this correct?  Should the cluster continue showing the last node to
> have
> > been alive for a partition as still in the ISR?
> >
> > Jason
> >
>

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