Currently there is no relation betweeen weak consistency and hadoop. I just
spent more time thinking about the requirement (as outlined below) a)
Maintain total of 3 data centers b) Maintain 1 copy per data center c)
If any data center goes down, dont create additional copies.
Above is not a valid model, especially requirement (c). Because this will take
away "Strong Consistency" model supported by Hadoop. Hope this explains.
I believe we can give up on requirement (c). I more currently exploring to see
whether anyway to achieve (a) and (b). Requirement (b) can also be relaxed to
have more copies per data center if needed
From: rahul.rec....@gmail.com
Date: Wed, 4 Sep 2013 10:04:49 +0530
Subject: Re: Multidata center support
To: user@hadoop.apache.org
Under replicated blocks are also consistent from a consumers point. Care of
explain the relation to weak consistency to hadoop.
Thanks,
Rahul
On Wed, Sep 4, 2013 at 9:56 AM, Rahul Bhattacharjee <rahul.rec....@gmail.com>
wrote:
Adam's response makes more sense to me to offline replicate generated data from
one cluster to another across data centers.
Not sure if configurable block placement block placement policy is supported in
Hadoop.If yes , then alone side with rack awareness , you should be able to
achieve the same.
I could not follow your question related to weak consistency.
Thanks,
Rahul
On Wed, Sep 4, 2013 at 2:20 AM, Baskar Duraikannu
<baskar.duraika...@outlook.com> wrote:
RahulAre you talking about rack-awareness script?
I did go through rack awareness. Here are the problems with rack awareness
w.r.to my (given) "business requirment"
1. Hadoop , default places two copies on the same rack and 1 copy on some
other rack. This would work as long as we have two data centers. if business
wants to have three data centers, then data would not be spread across.
Separately there is a question around whether it is the right thing to do or
not. I have been promised by business that they would buy enough bandwidth such
that each data center will be few milliseconds apart (in latency).
2. I believe Hadoop automatically re-replicates data if one or more node is
down. Assume when one out of 2 data center goes down. There will be a massive
data flow to create additional copies. When I say data center support, I
should be able to configure hadoop to say
a) Maintain 1 copy per data center b) If any data center goes down,
dont create additional copies.
Above requirements that I am pointing will essentially move hadoop from
strongly consistent to a week/eventual consistent model. Since this changes
fundamental architecture, it will probably break all sort of things... Might
not be possible ever in Hadoop.
Thoughts?
SadakIs there a way to implement above requirement via Federation?
ThanksBaskar
Date: Sun, 1 Sep 2013 00:20:04 +0530
Subject: Re: Multidata center support
From: visioner.sa...@gmail.com
To: user@hadoop.apache.org
What do you think friends I think hadoop clusters can run on multiple data
centers using FEDERATION
On Sat, Aug 31, 2013 at 8:39 PM, Visioner Sadak <visioner.sa...@gmail.com>
wrote:
The only problem i guess hadoop wont be able to duplicate data from one data
center to another but i guess i can identify data nodes or namenodes from
another data center correct me if i am wrong
On Sat, Aug 31, 2013 at 7:00 PM, Visioner Sadak <visioner.sa...@gmail.com>
wrote:
lets say that
you have some machines in europe and some in US I think you just need the ips
and configure them in your cluster set upit will work...
On Sat, Aug 31, 2013 at 7:52 AM, Jun Ping Du <j...@vmware.com> wrote:
Hi, Although you can set datacenter layer on your network topology, it is
never enabled in hadoop as lacking of replica placement and task scheduling
support. There are some work to add layers other than rack and node under
HADOOP-8848 but may not suit for your case. Agree with Adam that a cluster
spanning multiple data centers seems not make sense even for DR case. Do you
have other cases to do such a deployment?
Thanks,
Junping
From: "Adam Muise" <amu...@hortonworks.com>
To: user@hadoop.apache.org
Sent: Friday, August 30, 2013 6:26:54 PM
Subject: Re: Multidata center support
Nothing has changed. DR best practice is still one (or more) clusters per site
and replication is handled via distributed copy or some variation of it. A
cluster spanning multiple data centers is a poor idea right now.
On Fri, Aug 30, 2013 at 12:35 AM, Rahul Bhattacharjee <rahul.rec....@gmail.com>
wrote:
My take on this.
Why hadoop has to know about data center thing. I think it can be installed
across multiple data centers , however topology configuration would be required
to tell which node belongs to which data center and switch for block placement.
Thanks,
Rahul
On Fri, Aug 30, 2013 at 12:42 AM, Baskar Duraikannu
<baskar.duraika...@outlook.com> wrote:
We have a need to setup hadoop across data centers. Does hadoop support multi
data center configuration? I searched through archives and have found that
hadoop did not support multi data center configuration some time back. Just
wanted to see whether situation has changed.
Please help.
--
Adam MuiseSolution EngineerHortonworks
amuise@hortonworks.com416-417-4037
Hortonworks - Develops, Distributes and Supports Enterprise Apache Hadoop.
Hortonworks Virtual Sandbox
Hadoop: Disruptive Possibilities by Jeff Needham
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