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From: Roshni Rajagopal <Roshni.Rajagopal@wal-mart.com>
To: "user@cassandra.apache.org" <user@cassandra.apache.org>
Date: Wed, 1 Aug 2012 21:24:47 -0700
Subject: Re: Does Cassandra support operations in a transaction?
Thread-Topic: Does Cassandra support operations in a transaction?
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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 guarant=
ee 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and the latest will be returned, and no data will be out of date.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 a=
t a loss of performance- it will be fastest to just read and write once rat=
her 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 users receive out of date data (it isn't earth shattering if someone doesn=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 syste=
m where all entities must be consistently updated.

So designing in cassandra priortizes de-normalization. You cannot have refe=
rential integrity that 2 tables (col families in cassandra) are in sync bec=
ause the database has designed it to be so using foreign keys. The applicat=
ion needs to ensure that all data in column families are accurate and not o=
ut of sync, because data elements may be duplicated in different col famili=
es.


You cannot have 2 different entities and ensure that changes to both will b=
e 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>" <us=
er@cassandra.apache.org<mailto:user@cassandra.apache.org>>
To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cas=
sandra.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 na=
tively. Thats oen of the big compromises they make.  What they call "eventu=
al 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:wiwi1=
985@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


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