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From Jeffrey Kesselman <jef...@gmail.com>
Subject Re: Does Cassandra support operations in a transaction?
Date Thu, 02 Aug 2012 04:57:41 GMT
True consistancy, btw,  pretty much is only possible in a transactional
environment.

On Thu, Aug 2, 2012 at 12:56 AM, Jeffrey Kesselman <jeffpk@gmail.com> wrote:

> 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 compared and the latest will be returned, and no data will be out of date.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 some users receive out of date data (it isn't earth shattering if someone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.
>>
>> This email and any files transmitted with it are confidential and
>> intended solely for the individual or entity to whom they are addressed. If
>> you have received this email in error destroy it immediately. *** Walmart
>> Confidential ***
>>
>
>
>
> --
> It's always darkest just before you are eaten by a grue.
>



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

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