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From aaron morton <aa...@thelastpickle.com>
Subject Re: HintedHandoff
Date Thu, 09 May 2013 22:53:53 GMT
> ·        If node ‘X ‘ in DC1 which is a ‘replica’ node is down and a write comes
with CL =1 to DC1, the co-ordinator node will write the hint and also the data will be written
to the other ‘replica’ node in DC2 ? Is this correct ?
Writes always go to all UP replicas. So yes. 

> ·        If yes, then when we try to do a ‘read’ of this data with CL = ‘local_quorum’
from DC1, it will fail (since the data was written as a hint) and we will need to read it
from the other DC ?
It depends on your definition of fail. 
If node X is still down a read at LOCAL_QUORUM will fail to start and raise an UnavailableException.

If node X is up, but the hints have not been delivered, the read will proceed and return the
value before the write in step 1 above (including no value)

Cheers

-----------------
Aaron Morton
Freelance Cassandra Consultant
New Zealand

@aaronmorton
http://www.thelastpickle.com

On 9/05/2013, at 4:38 PM, Kanwar Sangha <kanwar@mavenir.com> wrote:

> Is this correct guys ?
>  
> From: Kanwar Sangha [mailto:kanwar@mavenir.com] 
> Sent: 07 May 2013 14:07
> To: user@cassandra.apache.org
> Subject: HintedHandoff
>  
> Hi -I had a question on  hinted-handoff.  We have 2 DCs configured with overall RF =
2 (DC1:1, DC2:1) and 4 nodes in each DC (total – 8 nodes across 2  DCs)
>  
> Now we do a write with CL = ONE and Hinted Handoff enabled.
>  
> ·        If node ‘X ‘ in DC1 which is a ‘replica’ node is down and a write comes
with CL =1 to DC1, the co-ordinator node will write the hint and also the data will be written
to the other ‘replica’ node in DC2 ? Is this correct ?
> ·        If yes, then when we try to do a ‘read’ of this data with CL = ‘local_quorum’
from DC1, it will fail (since the data was written as a hint) and we will need to read it
from the other DC ?
>  
> Thanks,
> Kanwar


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