Keep in mind there are side effects to increasing to RF = 4 - Storage requirements for each node will increase. Depending on the number of nodes in the cluster and the size of the data this could be significant. - Whilst the number of available coordinators increases, the number of nodes involved in QUORUM reads/writes will increase from 2 to 3.
On 24 March 2017 at 16:43, Alain Rastoul <alf.mmm....@gmail.com> wrote: > On 24/03/2017 01:00, Eric Stevens wrote: > >> Assuming an even distribution of data in your cluster, and an even >> distribution across those keys by your readers, you would not need to >> increase RF with cluster size to increase read performance. If you have >> 3 nodes with RF=3, and do 3 million reads, with good distribution, each >> node has served 1 million read requests. If you increase to 6 nodes and >> keep RF=3, then each node now owns half as much data and serves only >> 500,000 reads. Or more meaningfully in the same time it takes to do 3 >> million reads under the 3 node cluster you ought to be able to do 6 >> million reads under the 6 node cluster since each node is just >> responsible for 1 million total reads. >> >> Hi Eric, > > I think I got your point. > In case of really evenly distributed reads it may (or should?) not make > any difference, > > But when you do not distribute well the reads (and in that case only), > my understanding about RF was that it could help spreading the load : > In that case, with RF= 4 instead of 3, with several clients accessing keys > same key ranges, a coordinator could pick up one node to handle the request > in 4 replicas instead of picking up one node in 3 , thus having > more "workers" to handle a request ? > > Am I wrong here ? > > Thank you for the clarification > > > -- > best, > Alain > >
