Mailing-List: contact user-help@hadoop.apache.org; run by ezmlm
Precedence: bulk
Reply-To: user@hadoop.apache.org
Received-SPF: pass (nike.apache.org: domain of jing@hortonworks.com designates
 209.85.216.41 as permitted sender)
MIME-Version: 1.0
In-Reply-To: 
 <CANx3uAiap-PqVGRLa7QgTpEJH=LxTqC7pRkor0LuJ2bvbmZTJw@mail.gmail.com>
References: 
 <CANx3uAiVPmA3S6LXkO77k11ibCWjfSy2fzwAeKn=PrF2RVxXbw@mail.gmail.com>
 <CABGkNE9VsEObAQS2ze32v8SiP660Zq_su2rteh3Tf4a89og_5Q@mail.gmail.com>
 <CANx3uAiap-PqVGRLa7QgTpEJH=LxTqC7pRkor0LuJ2bvbmZTJw@mail.gmail.com>
From: Jing Zhao <jing@hortonworks.com>
Date: Tue, 15 Oct 2013 13:59:43 -0700
Message-ID: 
 <CABGkNE91FtSMv6dvdi7n+SL8YK=76cyqPoiP0gT6htDv_RRcFg@mail.gmail.com>
Subject: Re: high availability
To: user@hadoop.apache.org
Content-Type: text/plain; charset=US-ASCII

I think a real fencing is not required in case that you're using
QJM-based HA. If you are using ZKFC, a graceful fencing will first be
triggered in which ZKFC will send a RPC request to the original ANN to
make it standby. If the graceful fencing failed the configured fencing
will be used. In the worst case that your original ANN cannot
transition to standby state, QJM still has built-in single-writer
semantics (see https://issues.apache.org/jira/browse/HDFS-3862,
https://issues.apache.org/jira/browse/HDFS-4915). Thus you can set the
fence method to shell(/bin/true) (since in the current code the fence
configuration is still required).

On Tue, Oct 15, 2013 at 12:11 PM, Koert Kuipers <koert@tresata.com> wrote:
> 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
>>
>> --
>> CONFIDENTIALITY NOTICE
>> NOTICE: This message is intended for the use of the individual or entity
>> to
>> which it is addressed and may contain information that is confidential,
>> privileged and exempt from disclosure under applicable law. If the reader
>> of this message is not the intended recipient, you are hereby notified
>> that
>> any printing, copying, dissemination, distribution, disclosure or
>> forwarding of this communication is strictly prohibited. If you have
>> received this communication in error, please contact the sender
>> immediately
>> and delete it from your system. Thank You.
>
>

-- 
CONFIDENTIALITY NOTICE
NOTICE: This message is intended for the use of the individual or entity to 
which it is addressed and may contain information that is confidential, 
privileged and exempt from disclosure under applicable law. If the reader 
of this message is not the intended recipient, you are hereby notified that 
any printing, copying, dissemination, distribution, disclosure or 
forwarding of this communication is strictly prohibited. If you have 
received this communication in error, please contact the sender immediately 
and delete it from your system. Thank You.