https://en.wikipedia.org/wiki/Network_Time_Protocol
On Sun, Sep 6, 2015 at 8:23 AM, ibrahim El-sanosi <ibrahimsaba...@gmail.com> wrote: > Assume the Cassandra cluster is located in somewhere in US. Clients that > connect from different part of the world will have different timestamp (if > we rely on client timestamp to store write) or If a coordinator is > responsible for generating timestamp during the write, it also may have > different time among replicas, resulting in write conflict can occur and > impossible to resolve. > > > > When you are saying “Clocks should be synchronized”, does Cassandra > synchronize the clock if so how can you refer me to any related article? > > > > Regards, > > > > Ibrahim > > On Sun, Sep 6, 2015 at 1:23 PM, Daniel Schulz < > danielschulz2...@hotmail.com> wrote: > >> Cassandra is not changing clock settings; it does use it to omit TTL'ed >> rows in compaction phases. So make sure your nodes agree on the very same >> time using e.g. NTP. It is very crucial for data integrity on most >> distributed systems. >> >> ------------------------------ >> Date: Sun, 6 Sep 2015 13:10:14 +0100 >> Subject: Re: Is Cassandra really Strong consistency? >> From: ibrahimsaba...@gmail.com >> To: user@cassandra.apache.org >> >> >> Do you mean Cassandra does synchronize the clock across all the cluster, >> if yes how it does so, or could you refer me to any related article? >> >> Thank you >> >> >> Ibrahim >> >> On Sun, Sep 6, 2015 at 1:00 PM, Laing, Michael <michael.la...@nytimes.com >> > wrote: >> >> 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 >> >> >> >> >
