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From "Pierre Chalamet" <pie...@chalamet.net>
Subject Get CL ONE / NTS
Date Wed, 14 Sep 2011 13:33:12 GMT
Hello,

I have 2 datacenters. Cassandra is configured as follow:
- RackInferringSnitch
- NetworkTopologyStrategy for CF
- strategy_options: DC1:3 DC2:3

Data are written using CL LOCAL_QUORUM so data written from one datacenter will eventually
be replicated to the other datacenter. Data is always written exactly once. 

On the other side, I'd like to improve the read path. I'm using actually the CL ONE since
data is only written once (ie: timestamp is more or less meaningless in my case).

This is where I have some doubts: if data is written on DC1 and tentatively read from DC2
while the data is still not replicated or partially replicated (for whatever good reason since
replication is async), what is the behavior of Get with CL ONE / NTS ? 
1/ Will I have an error because DC2 does not have any copy of the data ? 
2/ Will Cassandra try to get the data from DC1 if nothing is found in DC2 ?
3/ In case of partial replication to DC2, will I see sometimes errors about servers not holding
the data in DC2 ?
4/ Does Get CL ONE failed as soon as the fastest server to answer tell it does not have the
data or does it waits until all servers tell they do not have the data ? 

Thanks a lot,
- Pierre
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