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From Lin Ma <lin...@gmail.com>
Subject Re: consistency, availability and partition pattern of HBase
Date Wed, 08 Aug 2012 15:47:48 GMT
And consistency is not sacrificed? i.e. all distributed clients' update
will results in sequential / real time update? Once update is done by one
client, all other client could see results immediately?

regards,
Lin

On Wed, Aug 8, 2012 at 11:17 PM, Mohit Anchlia <mohitanchlia@gmail.com>wrote:

> 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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