On Dec 9, 2010, at 18:50, Tyler Hobbs wrote: > If you switch your writes to CL ONE when a failure occurs, you might as well > use ONE for all writes. ONE and QUORUM behave the same when all nodes are > working correctly.
That's finally a precise statement! :) I was wondering what " to at least 1 replica's commit log" is supposed to actually mean: http://wiki.apache.org/cassandra/API Does quorum mean that data is replicated to q nodes or to at least q nodes? I just added another blank machine to my cluster. Nothing happened as expected (stopped writing to the cluster) but after I ran nodetool repair it held more data than all other nodes. So it copied data from the other nodes to this one? I assumed that data is replicated to q nodes not to all, is quorum 'only' about consistency and not about saving storage space? > - Tyler > > On Thu, Dec 9, 2010 at 11:26 AM, Timo Nentwig <timo.nent...@toptarif.de> > wrote: > > 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 > >>>> > >>>> > >>> > >> > >> > >
