Pawel, I think you've wandered into a real disconnect between how we communicate Riak replication, and how it actually works.
Although we say that N="nodes to replicate to", in reality, N="vnodes replicated to with every attempt to ensure they are different nodes with no guarantee". This is why you can have 3 nodes with 64 vnodes, and still set N>3. Now W is just the number of successful responses for a write to be considered a success. W can be any number less than or equal to N, but the difference will still be replicated as well, just asynchronously. For example, if N=3, W=2, once two nodes (well, vnodes) have responded, your write is considered a success. In the background, Riak will still ensure that third node is replicated to, giving you three total replicas. Hope that helps, Eric On Nov 12, 2012, at 3:01 PM, kamiseq <[email protected]> wrote: > this is funny but recently I started to think again about how riak works and > I thought I know more or less the basics ;] > > but I start digging and again I read > http://docs.basho.com/riak/latest/tutorials/fast-track/Tunable-CAP-Controls-in-Riak/ > and then made few tests with riak bucket configured as follows > > N = 3 > W = 3 > > I have 2 nodes running in my cluster so far (only 2 are connected) for test > and I can still write with hinted handoff. I updated the data and I wrote > again with same key - I got success. > > I changed properties on per request basis and I set w=1 I stopped first node > (so I had only one running) and put new key and value. I started first node > and query for the key and I got data from both nodes. I did the same with new > key again this time with w=3. and again it was successful. > > what is the real difference between N and W. if hinted handoff always save > data for later synchronisation can write ever fail. are there any differences > between first write and later updates. > > I hope it is not really stupid question > > pozdrawiam > Paweł Kamiński > > [email protected] > [email protected] > ______________________ > _______________________________________________ > riak-users mailing list > [email protected] > http://lists.basho.com/mailman/listinfo/riak-users_lists.basho.com
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