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From David Boxenhorn <da...@lookin2.com>
Subject Re: Taking down a node in a 3-node cluster, RF=2
Date Mon, 29 Nov 2010 08:41:30 GMT
For that matter, RF=1 and QUORUM are incompatible (if you want to be able to
take a node down).

In other words, if you use QUORUM, you need RF>=3.

On Sun, Nov 28, 2010 at 8:04 PM, Jake Luciani <jakers@gmail.com> wrote:

> Right.
>
>
> On Sun, Nov 28, 2010 at 1:03 PM, David Boxenhorn <david@lookin2.com>wrote:
>
>> OK. To sum up: RF=2 and QUORUM are incompatible (if you want to be able to
>> take a node down).
>>
>> Right?
>>
>> On Sun, Nov 28, 2010 at 7:59 PM, Jake Luciani <jakers@gmail.com> wrote:
>>
>>> I was wrong on this scenario and I'll explain where I was incorrect.
>>>
>>> Hints are stored for a downed node but they don't count towards meeting a
>>> consistency level.
>>> Let's take 2 scenarios:
>>>
>>> RF=6, Nodes=10
>>>
>>> If you READ/WRITE with CL.QUORUM you will need 4 alive nodes if one is
>>> down it will still have 4 active replicas to write to, one of these will
>>> store a hint and update the downed node when it comes back.
>>>
>>> RF=2, Nodes=3
>>>
>>> If you READ/WRITE with CL.QUORUM you need 2 live nodes.  If one of these
>>> 2 are down you can't meet the QUORUM level so the write will fail.
>>>
>>> In your scenario your best bet is to update to RF=3, then any two nodes
>>> will accept QUORUM
>>>
>>> Sorry for the confusion,
>>>
>>> -Jake
>>>
>>> On Sun, Nov 28, 2010 at 12:26 PM, David Boxenhorn <david@lookin2.com>wrote:
>>>
>>>> Thank you, Jake. It does... except that in another context you told me:
>>>>
>>>> Hints only happen when a node is unavailable and you are writing with
>>>> CL.ANY
>>>> If you never write with CL.ANY then you can turn off hinted handoff.
>>>>
>>>> How do I reconcile this?
>>>>
>>>>
>>>> On Sun, Nov 28, 2010 at 7:11 PM, Jake Luciani <jakers@gmail.com> wrote:
>>>>
>>>>> If you read/write data with quorum then you can safely take a node down
>>>>> in this scenario.  Subsequent writes will use hinted handoff to be passed
to
>>>>> the node when it comes back up.
>>>>>
>>>>> More info is here: http://wiki.apache.org/cassandra/HintedHandoff
>>>>>
>>>>> Does that answer your question?
>>>>>
>>>>> -Jake
>>>>>
>>>>>
>>>>> On Sun, Nov 28, 2010 at 9:42 AM, Ran Tavory <rantav@gmail.com>
wrote:
>>>>>
>>>>>> to me it makes sense that if hinted handoff is off then cassandra
>>>>>> cannot satisfy 2 out of every 3rd writes writes when one of the nodes
is
>>>>>> down since this node is the designated node of 2/3 writes.
>>>>>> But I don't remember reading this somewhere. Does hinted handoff
>>>>>> affect David's situation?
>>>>>> (David, did you disable HH in your storage-config?
>>>>>> <HintedHandoffEnabled>false</HintedHandoffEnabled>)
>>>>>>
>>>>>>
>>>>>> On Sun, Nov 28, 2010 at 4:32 PM, David Boxenhorn <david@lookin2.com>wrote:
>>>>>>
>>>>>>> For the vast majority of my data usage eventual consistency is
fine
>>>>>>> (i.e. CL=ONE) but I have a small amount of critical data for
which I read
>>>>>>> and write using CL=QUORUM.
>>>>>>>
>>>>>>> If I have a cluster with 3 nodes and RF=2, and CL=QUORUM does
that
>>>>>>> mean that a value can be read from or written to any 2 nodes,
or does it
>>>>>>> have to be the particular 2 nodes that store the data? If it
is the
>>>>>>> particular 2 nodes that store the data, that means that I can't
even take
>>>>>>> down one node, since it will be the mandatory 2nd node for 1/3
of my data...
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> /Ran
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>

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