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From Jake Luciani <jak...@gmail.com>
Subject Re: Taking down a node in a 3-node cluster, RF=2
Date Sun, 28 Nov 2010 18:04:24 GMT
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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