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From Koert Kuipers <ko...@tresata.com>
Subject Re: high availability
Date Tue, 15 Oct 2013 19:11:51 GMT
Jing,
thanks for your answer.

if hbase with high availability is the desired goal, is it recommended to
remove sshfence? we do not plan to use hdfs for anything else.

i understood that the only downside of no fencing is that the old namenode
could still be serving read requests. could this negatively impact hbase
functionality, or worse, could it corrupt hbase somehow (not sure how that
would be...)?

thanks! koert



On Tue, Oct 15, 2013 at 12:38 AM, Jing Zhao <jing@hortonworks.com> wrote:

> "it is unclear to me if the transition in this case is also rapid but
> the fencing takes long while the new namenode is already active, or if
> in this period i am stuck without an active namenode."
>
> The standby->active transition will get stuck in this period, i.e.,
> the NN can only become active after fencing the old active NN. During
> this period since the only NN is in standby state which cannot handle
> usual R/W operations and just throws StandbyException, hbase region
> server may kill itself in some cases I guess.
>
> I think you can remove sshfence from the configuration if you are
> using QJM-based HA.
>
> On Fri, Oct 11, 2013 at 4:51 PM, Koert Kuipers <koert@tresata.com> wrote:
> > i have been playing with high availability using journalnodes and 2
> masters
> > both running namenode and hbase master.
> >
> > when i kill the namenode and hbase-master processes on the active master,
> > the failover is perfect. hbase never stops and a running map-reduce jobs
> > keeps going. this is impressive!
> >
> > however when instead of killing the proceses i kill the entire active
> master
> > machine, the transactions is less smooth and can take a long time, at
> least
> > it seems this way in the logs. this is because ssh fencing fails but
> keeps
> > trying. my fencing is configured as:
> >
> >  <property>
> >     <name>dfs.ha.fencing.methods</name>
> >     <value>
> >       sshfence
> >       shell(/bin/true)
> >     </value>
> >     <final>true</final>
> >   </property>
> >
> > it is unclear to me if the transition in this case is also rapid but the
> > fencing takes long while the new namenode is already active, or if in
> this
> > period i am stuck without an active namenode. it is hard to accurately
> test
> > this in my setup.
> > is this supposed to take this long? is HDFS writable in this period? and
> is
> > hbase supposed to survive this long transition?
> >
> > thanks! koert
>
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