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From "Jack Krupansky" <j...@basetechnology.com>
Subject Re: All writes fail with ONE consistency level when adding second node to cluster?
Date Wed, 23 Jul 2014 20:20:02 GMT
Granted, for “normal” apps it is unlikely to be appropriate but...

>From an old post by Jonathan:
---
Extreme write availability

For applications that want Cassandra to accept writes even when all the normal replicas are
down (so even ConsistencyLevel.ONE cannot be satisfied), Cassandra provides ConsistencyLevel.ANY.
ConsistencyLevel.ANY guarantees that the write is durable and will be readable once an appropriate
replica target becomes available and receives the hint replay.
---
See:
http://www.datastax.com/dev/blog/understanding-hinted-handoff

I can think of a couple of use cases: sensor data where the devices are streaming frequently,
so losing a reading is not a big deal because another reading is coming soon anyway, and a
Twitter firehose where you are after a robust sample rather than absolute consistency. Minimizing
network latency may be a bigger deal than whether immediate queries can see the data.

And as the description notes, hinted handoff will eventually propagate the data (unless it
times out and drops the hint.)

-- Jack Krupansky

From: Robert Coli 
Sent: Wednesday, July 23, 2014 1:15 PM
To: user@cassandra.apache.org 
Cc: Kevin Burton 
Subject: Re: All writes fail with ONE consistency level when adding second node to cluster?

On Tue, Jul 22, 2014 at 7:46 PM, Andrew <redmumba@gmail.com> wrote:

ONE means write to one replica (in addition to the original).  If you want to write to any
of them, use ANY.  Is that the right understanding?


This has come up a few times, so let me be unambiguous about when to use CL.ANY :

NEVER EVER USE CL.ANY. IT ALMOST CERTAINLY SHOULD NOT EVEN EXIST.

IF YOU THINK YOU NEED TO USE IT, YOU ARE ALMOST CERTAINLY WRONG.

;D

=Rob

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