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From Jeffrey Kesselman <jef...@gmail.com>
Subject Re: Does Cassandra support operations in a transaction?
Date Thu, 02 Aug 2012 04:56:32 GMT
Roshni,

Thats not what consistancy in ACID means.  Its not consistancy of reading
the ame data, its referntial integrity between related pecies of data.

"Consistency
Data is in a consistent state when a transaction starts and when it ends. For
example, in an application that transfers funds from one account to
another, the consistency property ensures that the total value of funds in
both the accounts is the same at the start and end of each transaction. "
http://publib.boulder.ibm.com/infocenter/cicsts/v3r2/index.jsp?topic=%2Fcom.ibm.cics.ts.productoverview.doc%2Fconcepts%2Facid.html

A lot of people i nthe NoSql wqorld use the term "consistancy" when what
they mean is "durability."

" Durability After a transaction successfully completes, changes to data
persist and are not undone, even in the event of a system failure. "

Many NoSql databses (includiogn Cassandra) are eventuallydurable, in the
sense that a read immediately after a write may noit reflect that write,
but at soem l;ater point, it will.

None p[rovide true consistancy that I am aware of.



:

On Thu, Aug 2, 2012 at 12:24 AM, Roshni Rajagopal <
Roshni.Rajagopal@wal-mart.com> wrote:

> Hi Ivan,
>
> Cassandra supports 'tunable consistency' . If you always read and write at
> a quorum (or local quorum for multi data center) from one , you can
> guarantee that the results will be consistent as in all the data will be
> compared and the latest will be returned, and no data will be out of date.
> This is at a loss of performance- it will be fastest to just read and write
> once rather than check a quorum of nodes.
>
> What you chose depends on what your application needs are. Is it ok if
> some users receive out of date data (it isn't earth shattering if someone
> doesn't know what you're eating right now), or is it a banking transaction
> system where all entities must be consistently updated.
>
> So designing in cassandra priortizes de-normalization. You cannot have
> referential integrity that 2 tables (col families in cassandra) are in sync
> because the database has designed it to be so using foreign keys. The
> application needs to ensure that all data in column families are accurate
> and not out of sync, because data elements may be duplicated in different
> col families.
>
>
> You cannot have 2 different entities and ensure that changes to both will
> be done and then only be visible to others.
>
>
> Regards,
>
>
> From: Jeffrey Kesselman <jeffpk@gmail.com<mailto:jeffpk@gmail.com>>
> Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <
> user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
> To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <
> user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
> Subject: Re: Does Cassandra support operations in a transaction?
>
> Short story is that few if any of the NoSql systems supprot transactions
> natively. Thats oen of the big compromises they make.  What they call
> "eventual consistancy" is actually eventual Durabiltiy in ACID terms.
>
> Consistancy, as meant by the C in ACID,  is not gauranteed at all.
>
> On Wed, Aug 1, 2012 at 6:21 AM, Ivan Jiang <wiwi1985@gmail.com<mailto:
> wiwi1985@gmail.com>> wrote:
> Hi,
>     I am a new guy to Cassandra, I wonder if available to call Cassandra
> in one Transaction such as in Relation-DB.
>
> Thanks in advance.
>
> Best Regards,
> Ivan Jiang
>
>
>
> --
> It's always darkest just before you are eaten by a grue.
>
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>



-- 
It's always darkest just before you are eaten by a grue.

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