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HBase, mail # user - consistency, availability and partition pattern of HBase


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Re: consistency, availability and partition pattern of HBase
Wei Tan 2012-08-08, 04:18
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
[EMAIL PROTECTED]; 914-784-6752

From:   Lin Ma <[EMAIL PROTECTED]>
To:     [EMAIL PROTECTED],
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