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From Lucas Nodine <lucasnod...@gmail.com>
Subject Re: Curious as to how Cassandra handles the following
Date Sun, 26 Sep 2010 23:01:40 GMT
Ok, so based on everyone's input it seems that I need to put some sort of
server in front of Cassandra to handle locking and exclusive access.

I am planning on building a system (DMS) that will store resources
(document, images, media, etc) using Cassandra for data.  As my target user
is going to be someone without any understanding of a 'diff' I have elected
for locking instead of conflict resolution in versions.  This means I
require a method of exclusive access.  Suggestions have been Cage and
Zookeeper, I'm going to be writting this is C# for .net and mono.  Any other
suggestions besides just building a simple solution?

I currently have an application sitting between the end client and Cassandra
to handle business logic, by the sound of it I should just implement a
method of communication between however many "servers" I will have (it will
support distributed deployment) to apply a lock to the resource, system
wide.

I understand the technical aspects of how that should work; however, before
I begin that, does anyone have any suggestions or tips?

Thanks,

- Lucas Nodine




On Sun, Sep 26, 2010 at 4:34 PM, Jonathan Ellis <jbellis@gmail.com> wrote:

> Atomic (all of it will complete, or none), but not isolated (readers
> can see parts of a write before they see the whole thing).
>
> On Sun, Sep 26, 2010 at 1:19 PM, Aaron Morton <aaron@thelastpickle.com>
> wrote:
> > Mutations against a single key on a single machine are
> > atomic http://wiki.apache.org/cassandra/FAQ#batch_mutate_atomic
> >
> > Aaron
> > On 27 Sep, 2010,at 07:48 AM, Norman Maurer <norman@apache.org> wrote:
> >
> > To be more clear (maybe I was not before). BatchMutate is not atomic.
> > So it only "batch up" mutates to reduce overhead. So it can be that
> > you will receive data from it even if the whole operation is not
> > complete or will not complete.
> >
> > bye,
> > Norman
> >
> >
> > 2010/9/26 Norman Maurer <norman@apache.org>:
> >> Comments inside..
> >>
> >> 2010/9/26 Lucas Nodine <lucasnodine@gmail.com>:
> >>> I'm looking at a design where multiple clients will connect to
> Cassandra
> >>> and
> >>> get/mutate resources, possibly concurrently.  After planning a bit, I
> ran
> >>> into the following scenero for which I have not been able to research
> to
> >>> find an answer sufficient for my needs.  I have found where others have
> >>> recommended Zookeeper for such tasks, but I want to determine if there
> is
> >>> a
> >>> simple solution before including another product in my design.
> >>>
> >>> Make the following assumption for all following situations:
> >>> Assuming multiple clients where a client is someone accessing Cassandra
> >>> using thrift.  All reads and writes are performed using the QUORUM
> >>> consistency level.
> >>>
> >>> Situation 1:
> >>> Client A ("A") connects to Cassandra and requests a QUORUM consistency
> >>> level
> >>> get of an entire row.  At or very shortly thereafter (before A's
> request
> >>> completes), Client B ("B") connects to Cassandra and inserts (or
> mutates)
> >>> a
> >>> column (or multiple columns) within the row.
> >>>
> >>> Does A receive the new data saved by B or does A receive the data prior
> >>> to
> >>> B's save?
> >>
> >> Shoud receive A stuff.
> >>>
> >>> Situaton 2:
> >>> B connects and mutates multiple columns within a row.  A requests some
> >>> data
> >>> therein while B is processing.
> >>>
> >>> Result?
> >>
> >> Depends.. is it done in BatchMutate or not ?
> >>
> >>>
> >>> Situation 3:
> >>> B mutates multiple columns within multiple rows.  A requests some data
> >>> therein while B is processing.
> >>>
> >>> Result?
> >>
> >> See above..
> >>
> >>>
> >>> Justification: At certain points I want to essentially lock a resource
> >>> (row)
> >>> in cassandra for exclusive write access (think checkout a resource) by
> >>> setting a flag value of a column within that row.  I'm just considering
> >>> race
> >>> conditions.
> >>>
> >> You will need to use cages or something like that..
> >>
> >>
> >>> Thanks,
> >>>
> >>> Lucas Nodine
> >>
> >> Bye,
> >> Norman
> >>
> >
>
>
>
> --
> Jonathan Ellis
> Project Chair, Apache Cassandra
> co-founder of Riptano, the source for professional Cassandra support
> http://riptano.com
>



-- 
Lucas J. Nodine
Assistant Labette County Attorney
201 S. Central, Suite B
Parsons, KS 67357
(620) 421-6370

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