@ibrahim: When saying "clocks should be synchronized", it includes Cassandra nodes AND clients
NTP is the way to go Le 6 sept. 2015 à 14:56, Laing, Michael <michael.la...@nytimes.com<mailto:michael.la...@nytimes.com>> a écrit : https://en.wikipedia.org/wiki/Network_Time_Protocol On Sun, Sep 6, 2015 at 8:23 AM, ibrahim El-sanosi <ibrahimsaba...@gmail.com<mailto: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<mailto: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<mailto:ibrahimsaba...@gmail.com> To: user@cassandra.apache.org<mailto: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<mailto: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<mailto: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
