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Date: Sun, 12 Feb 2012 10:00:07 +0100
From: Eric Charles <eric@apache.org>
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To: user@hbase.apache.org
Subject: Re: Which server store the root and .meta. information?
References: <CB5C26E9.24641%doug.meil@explorysmedical.com>
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Hi Doug,

I was well thinking that master was in the play in case of region split
or problems.
I searched in the paper book I have, but didn't really find anything on
that.

Luckily, it is well documented on
http://hbase.apache.org/book/regions.arch.html:

- failover: "... The Master will detect that the RegionServer has failed. "
- split: "...and then reports the split to the Master. "

So master seems also to be involved in a regular splitting in addition
to RS lose. More questions:

1.- What occurs if the region server can not report to Master after
splitting (for example if a guy like me killed the master to see 'what
happens'...).
2.- How does the master achieve the monitoring of its regions? (is there
an hearbeat generated by the regions or does Master pol).

(searched around in books... but didn't find, maybe something to do with
CatalogJanitor?)

Thx,
Eric

On 11/02/12 20:12, Doug Meil wrote:
> 
> Regarding the master being down, just be aware that if you lose an RS that
> you'll have issues because the master is what does the reassignment.  Per
> the previous comments, at steady-state HBase can run without the master -
> there's an asterisk.
> 
> 
> 
> 
> On 2/11/12 11:31 AM, "Eric Charles"<eric@apache.org>  wrote:
> 
>> Funky, cause HBase is often presented as a 3-layers server model
>> zookeeper/master/region (root/meta in the regions bringing still more
>> fogs).
>>
>> Maybe the commonly understanding in the community is that HBase's
>> HMaster is like Hadoop's NameNode, which is not the case (NameNode's
>> failure will bring your cluster down, HMaster's failure will not...).
>>
>> Upon presentation simplification (via 'master' renaming, or at least via
>> explanation emphases), having a more simple model such as the one
>> described in HBASE-3171 could help (this is my very short opinion, I
>> remember having read valid arguments against that model).
>>
>> client<->zk<->(master)<->region(root|master)
>> or
>> client<->zk<->region (+admin)
>>
>> the latter looks simpler, doesn't it?
>>
>>
>> Thx,
>>
>> Eric
>>
>> On 11/02/12 16:45, Stack wrote:
>>> 2012/2/11 Eric Charles<eric@apache.org>:
>>>> Hypothetical case (probably asked a number of time here, sorry...):
>>>>
>>>> Can a client correcty put, get, scan (no admins tasks such as create
>>>> table,...) with a HBase cluster having its HMaster process down  ?
>>>>
>>>
>>> It can Eric.   Kill your master and you can do all the above.
>>> St.Ack
>>
>> -- 
>> eric | http://about.echarles.net | @echarles
>>
> 
> 

-- 
eric | http://about.echarles.net | @echarles