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


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Lin Ma 2012-08-08, 01:28
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Wei Tan 2012-08-08, 04:18
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J Mohamed Zahoor 2012-08-08, 04:56
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Lin Ma 2012-08-08, 06:56
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Mohit Anchlia 2012-08-08, 15:17
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Lin Ma 2012-08-08, 15:47
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lars hofhansl 2012-08-09, 01:31
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Lin Ma 2012-08-09, 02:32
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Re: consistency, availability and partition pattern of HBase
Bryan Beaudreault 2012-08-09, 03:09
Actual data backing hbase is replicated, but that is handled by HDFS.  Yes,
if you lose an hdfs datanode, clients (in this case the client is hbase)
move to the next node in the pipeline.

However, only a single RegionServer ever hosts a region at once.  If the
RegionServer dies, there is a period where the master must notice the
regions are unhosted and move them to other regionservers.  During that
period, data is inaccessible or modifiable.

On Wed, Aug 8, 2012 at 10:32 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?
>
> 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
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lars hofhansl 2012-08-09, 04:21
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Lin Ma 2012-08-09, 05:34
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Amandeep Khurana 2012-08-09, 06:04
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Lin Ma 2012-08-09, 08:18
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Amandeep Khurana 2012-08-09, 08:43
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Amandeep Khurana 2012-08-09, 05:34
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Lin Ma 2012-08-09, 05:38
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Amandeep Khurana 2012-08-09, 05:41
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Lin Ma 2012-08-09, 08:15
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Mohit Anchlia 2012-08-09, 05:23