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From: "Jack Krupansky" <jack@basetechnology.com>
To: <user@cassandra.apache.org>
References: <543565EE.4040904@cs.rutgers.edu>
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In-Reply-To: <5435C670.7030707@cs.rutgers.edu>
Subject: Re: Consistency Levels
Date: Thu, 9 Oct 2014 00:26:28 -0400
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Sender: "Jack Krupansky" <jack@basetechnology.com>

It would certainly depend on the nuances of your definitions! Especially 
since you added this monster of a caveat: " in the absence of failures".

Here's a scenario for you: 1) Write at quorum, 2) Add 3 nodes, 3) 
Immediately read at [the new] quorum - no guarantee that the new nodes will 
have fully bootstrapped.

Who knows how many other modalities there might be - despite however many 
caveats you want to tack on.

"Strong consistency" is a "model", not necessarily a reality at any point in 
time even if it was a reality at a prior point in time.

If I deliberately "decommission" a node, that isn't necessarily a "failure" 
is it?

All of that said, "it depends" on where you're trying to get to.

-- Jack Krupansky

-----Original Message----- 
From: William Katsak
Sent: Wednesday, October 8, 2014 7:19 PM
To: user@cassandra.apache.org
Subject: Re: Consistency Levels

Thanks.

I am thinking more in terms of the combination of read/write. If I am
correct, QUORUM reads and QUORUM writes (or ONE-ALL) should deliver
strong consistency in the absence of failures, correct? Or this this
still considered eventual consistency, somehow?

-Bill


On 10/08/2014 06:17 PM, Jack Krupansky wrote:
> I don't know of any such data collected by DataStax - it's not like
> we're the NSA, sniffing all requests.
>
> ONE is certainly fast, but only fine if you don't have immediate need to
> read the data or don't need the absolutely most recent value.
>
> To be clear, even QUORUM write is eventual consistency - to all nodes
> beyond the immediate quorum.
>
> -- Jack Krupansky
>
> -----Original Message----- From: William Katsak
> Sent: Wednesday, October 8, 2014 12:27 PM
> To: user@cassandra.apache.org
> Subject: Consistency Levels
>
> Hello,
>
> I was wondering if anyone (Datastax?) has any usage data about
> consistency levels. For example, what consistency levels are real
> applications using in real production scenarios. Who is using eventual
> consistency (ONE-ONE) in production vs strong consistency
> (QUORUM-QUORUM, ONE-ALL). Obviously it depends on the application, but I
> am trying to collect some information on this.
>
> I saw the talk from Christos Kalantzis (from Cassandra13 I think) about
> Netflix using eventual consistency, but I was wondering if there is any
> more data out there.
>
> Thanks in advance,
>
> Bill Katask
> Ph.D. Student
> Department of Computer Science
> Rutgers University

-- 
****************************************
William Katsak <wkatsak@cs.rutgers.edu>
Ph.D. Student
Rutgers University
Department of Computer Science
****************************************