On Dec 9, 2010, at 17:55, Sylvain Lebresne wrote: >> I naively assume that if I kill either node that holds N1 (i.e. node 1 or >> 3), N1 will still remain on another node. Only if both fail, I actually lose >> data. But apparently this is not how it works... > > Sure, the data that N1 holds is also on another node and you won't > lose it by only losing N1. > But when you do a quorum query, you are saying to Cassandra "Please > please would you fail my request > if you can't get a response from 2 nodes". So if only 1 node holding > the data is up at the moment of the > query then Cassandra, which is a very polite software, do what you > asked and fail.
And my application would fall back to ONE. Quorum writes will also fail so I would also use ONE so that the app stays up. What would I have to do make the data to redistribute when the broken node is up again? Simply call nodetool repair on it? > If you want Cassandra to send you an answer with only one node up, use > CL=ONE (as said by David). > >> >>> On Thu, Dec 9, 2010 at 6:05 PM, Sylvain Lebresne <sylv...@yakaz.com> wrote: >>> I'ts 2 out of the number of replicas, not the number of nodes. At RF=2, you >>> have >>> 2 replicas. And since quorum is also 2 with that replication factor, >>> you cannot lose >>> a node, otherwise some query will end up as UnavailableException. >>> >>> Again, this is not related to the total number of nodes. Even with 200 >>> nodes, if >>> you use RF=2, you will have some query that fail (altough much less that >>> what >>> you are probably seeing). >>> >>> On Thu, Dec 9, 2010 at 5:00 PM, Timo Nentwig <timo.nent...@toptarif.de> >>> wrote: >>>> >>>> On Dec 9, 2010, at 16:50, Daniel Lundin wrote: >>>> >>>>> Quorum is really only useful when RF > 2, since the for a quorum to >>>>> succeed RF/2+1 replicas must be available. >>>> >>>> 2/2+1==2 and I killed 1 of 3, so... don't get it. >>>> >>>>> This means for RF = 2, consistency levels QUORUM and ALL yield the same >>>>> result. >>>>> >>>>> /d >>>>> >>>>> On Thu, Dec 9, 2010 at 4:40 PM, Timo Nentwig <timo.nent...@toptarif.de> >>>>> wrote: >>>>>> Hi! >>>>>> >>>>>> I've 3 servers running (0.7rc1) with a replication_factor of 2 and use >>>>>> quorum for writes. But when I shut down one of them >>>>>> UnavailableExceptions are thrown. Why is that? Isn't that the sense of >>>>>> quorum and a fault-tolerant DB that it continues with the remaining 2 >>>>>> nodes and redistributes the data to the broken one as soons as its up >>>>>> again? >>>>>> >>>>>> What may I be doing wrong? >>>>>> >>>>>> thx >>>>>> tcn >>>> >>>> >>> >> >>
