On Fri, Jul 17, 2009 at 3:58 PM, Vijay<vijay2...@gmail.com> wrote: > Still confused, > > If i have a Quorum Write with block for to be 3 and 2 of them are alive i > will write to 3 nodes with HH right?
yes, but only 2 will be available for reads, so the 3rd can't count towards fulfulling block_for. the semantics of block_for on read (R) and write (W) are that you have strong consistency if R + W >= N where N is number of replicas. (see http://www.allthingsdistributed.com/2007/12/eventually_consistent.html) For this to hold in cassandra, we need to provide consistency where (for instance) W = N and R = 1. Remember that a HH write is not available for reads. This means that we need to fail the write if we can't write the full N replicas to the right nodes. (This is why quorum write + quorum read is often a better tradeoff in practice since you can tolerate node failures w/o losing availability.) -Jonathan > During query it will fail if i only have block for to be 3? > > Regards, > </VJ> > > > > > On Fri, Jul 17, 2009 at 1:36 PM, Jonathan Ellis <jbel...@gmail.com> wrote: >> >> ck_for to zero, then writes will indeed never fail >> (unless the node the client is ta >
