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Re: consistency, availability and partition pattern of HBase
On Wed, Aug 8, 2012 at 7:32 PM, Lin Ma <[EMAIL PROTECTED]> wrote:

> Thank you Lars.
>
> Is the same data store duplicated copy across region server? If so, if one
> primary server for the region dies, client just need to read from the
> secondary server for the same region. Why there is data is unavailable
> time?
>
>
To get better understanding of this I suggest looking at how the WAL logs
are stored. WAL stores multiple regions in one log. Before region is alive
on other region server master needs to split the logs so that it can
replayed by the region server. This process causes downtime with respect to
the region which is being replayed using edit logs.
> BTW: please feel free to correct me for any wrong knowledge about HBase.
>
> regards,
> Lin
>
> On Thu, Aug 9, 2012 at 9:31 AM, lars hofhansl <[EMAIL PROTECTED]> wrote:
>
> > After a write completes the next read (regardless of the location it is
> > issued from) will see the latest value.
> > This is because at any given time exactly RegionServer is responsible for
> > a specific Key
> > (through assignment of key ranges to regions and regions to
> RegionServers).
> >
> >
> > As Mohit said, the trade off is that data is unavailable if a
> RegionServer
> > dies until another RegionServer picks up the regions (and by extension
> the
> > key range)
> >
> > -- Lars
> >
> >
> > ----- Original Message -----
> > From: Lin Ma <[EMAIL PROTECTED]>
> > To: [EMAIL PROTECTED]
> > Cc:
> > Sent: Wednesday, August 8, 2012 8:47 AM
> > Subject: Re: consistency, availability and partition pattern of HBase
> >
> > 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 <[EMAIL PROTECTED]
> > >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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> 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
> > > >> [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