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From Andrey Ilinykh <ailin...@gmail.com>
Subject Re: Clarification on how multi-DC replication works
Date Tue, 11 Feb 2014 18:02:08 GMT
1. reply part is missing.
2. It is confusing a little bit. I would not use term "synchronous".
Everything is asynchronous here. Coordinator writes data to all local nodes
and waits for  response from ANY two of them (in case of quorum). In your
picture it looks like the coordinator first makes decision what nodes
should reply. It is not correct.


On Tue, Feb 11, 2014 at 9:36 AM, Mullen, Robert
<robert.mullen@pearson.com>wrote:

> So is that picture incorrect, or just incomplete missing the piece on how
> the nodes reply to the coordinator node.
>
>
> On Tue, Feb 11, 2014 at 9:38 AM, sankalp kohli <kohlisankalp@gmail.com>wrote:
>
>> @Mullen,
>> I think your diagram does not answer the question on responses.
>> @Sameer
>> All nodes in DC2 will replay back to the co-ordinator in DC1. So if you
>> have replication of DC1:3,DC2:3. A co-ordinator node will get 6 responses
>> back if it is not in the replica set.
>> Hope that answers your question.
>>
>>
>> On Tue, Feb 11, 2014 at 8:16 AM, Mullen, Robert <
>> robert.mullen@pearson.com> wrote:
>>
>>> I had the same question a while back and put together this picture to
>>> help me understand the flow of data for multi region deployments. Hope that
>>> it helps.
>>>
>>>
>>> On Mon, Feb 10, 2014 at 7:52 PM, Sameer Farooqui <sameer@blueplastic.com
>>> > wrote:
>>>
>>>> Hi,
>>>>
>>>> I was hoping someone could clarify a point about multi-DC replication.
>>>>
>>>> Let's say I have 2 data centers configured with replication factor = 3
>>>> in each DC.
>>>>
>>>> My client app is sitting in DC 1 and is able to intelligently pick a
>>>> coordinator that will also be a replica partner.
>>>>
>>>> So the client app sends a write with consistency for DC1 = Q and
>>>> consistency for DC2 = Q to a coordinator node in DC1.
>>>>
>>>> That coordinator in DC1 forwards the write to 2 other nodes in DC1 and
>>>> a coordinator in DC2.
>>>>
>>>> Is it correct that all 3 nodes in DC2 will respond back to the original
>>>> coordinator in DC1? Or will the DC2 nodes respond back to the DC2
>>>> coordinator?
>>>>
>>>> Let's say one of the replica nodes in DC2 is down. Who will hold the
>>>> hint for that node? The original coordinator in DC1 or the coordinator in
>>>> DC2?
>>>>
>>>
>>>
>>
>

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