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From Mohit Anchlia <mohitanch...@gmail.com>
Subject Re: consistency, availability and partition pattern of HBase
Date Wed, 08 Aug 2012 15:17:14 GMT
I think availability is sacrificed in the sense that if region server fails clients will have
data inaccessible for the time region comes up on some other server, not to confuse with data
loss.

Sent from my iPad

On Aug 7, 2012, at 11:56 PM, Lin Ma <linlma@gmail.com> wrote:

> Thank you Wei!
> 
> Two more comments,
> 
> 1. How about Hadoop's CAP characters do you think about?
> 2. For your comments, if HBase implements "per key sequential consistency",
> what are the missing characters for consistency? Cross-key update
> sequences? Could you show me an example about what you think are missed?
> thanks.
> 
> regards,
> Lin
> 
> On Wed, Aug 8, 2012 at 12:18 PM, Wei Tan <wtan@us.ibm.com> wrote:
> 
>> Hi Lin,
>> 
>> In the CAP theorem
>> Consistency stands for atomic consistency, i.e., each CRUD operation
>> occurs sequentially in a global, real-time clock
>> Availability means each server if not partitioned can accept requests
>> 
>> Partition means network partition
>> 
>> As far as I understand (although I do not see any official documentation),
>> HBase achieved "per key sequential consistency", i.e., for a specific key,
>> there is an agreed sequence, for all operations on it. This is weaker than
>> strong or sequential consistency, but stronger than "eventual
>> consistency".
>> 
>> BTW: CAP was proposed by Prof. Eric Brewer...
>> http://en.wikipedia.org/wiki/Eric_Brewer_%28scientist%29
>> 
>> Best Regards,
>> Wei
>> 
>> Wei Tan
>> Research Staff Member
>> IBM T. J. Watson Research Center
>> 19 Skyline Dr, Hawthorne, NY  10532
>> wtan@us.ibm.com; 914-784-6752
>> 
>> 
>> 
>> From:   Lin Ma <linlma@gmail.com>
>> To:     user@hbase.apache.org,
>> Date:   08/07/2012 09:30 PM
>> Subject:        consistency, availability and partition pattern of HBase
>> 
>> 
>> 
>> Hello guys,
>> 
>> According to the notes by Werner*, "*He presented the CAP theorem, which
>> states that of three properties of shared-data systems—data consistency,
>> system availability, and tolerance to network partition—only two can be
>> achieved at any given time." =>
>> http://www.allthingsdistributed.com/2008/12/eventually_consistent.html
>> 
>> But it seems HBase could achieve all of the 3 features at the same time.
>> Does it mean HBase breaks the rule by Werner. :-)
>> 
>> If not, which one is sacrificed -- consistency (by using HDFS),
>> availability (by using Zookeeper) or partition (by using region / column
>> family) ? And why?
>> 
>> regards,
>> Lin
>> 
>> 
>> 

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