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From Daniel Schulz <danielschulz2...@hotmail.com>
Subject RE: Is Cassandra really Strong consistency?
Date Sun, 06 Sep 2015 12:23:14 GMT
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: ibrahimsabattt@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.laing@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 <ibrahimsabattt@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




 		 	   		  
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