I think I saw this before. Clocks must be synchronized.
On Sun, Sep 6, 2015 at 7:28 AM, ibrahim El-sanosi <ibrahimsaba...@gmail.com> wrote: > Hi folks, > > Assume we have 4-nodes cluster N1, N2, N3, and N4 and replication factor > is 3. When write CL =ALL and read CL=ONE: > > Client c1 sends W1 = [k1,V1] to N1 (a coordinator). A coordinator (N1) > generates timestamp Mon 05-09-2015 11:30:40,200 (according to its local > clock) and assigned it to W1 and sends the W1 to N2, N3, and N4. After few > seconds, Client c2 sends W2 = [K1, V2] to N4 (a coordinator). A coordinator > (N4) generates timestamp Mon 05-09-2015 11:30:38,200 (according to its > local clock, but assume here N4 clock a bit behind, nearly 2 seconds) and > assigned it to W2 and sends the W2 to N2, N3, and N4 (itself). > > As we have write CL =ALL and read CL = ONE. Now, Client c2 wants to read > K1, connects to a coordinator N1, a coordinator sends read K1 to N2, > picking latest timestamp which is [K1, V1]:Mon 05-09-2015 11:30:40,200. > > So in this scenario, the latest data that wrote to the replicas is [K1, > V2] which should be the correct one, but it reads [K1,V1] because of divert > clock. > > Can such scenario occur? > > Thank you >
