cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Laing, Michael" <michael.la...@nytimes.com>
Subject Re: Is Cassandra really Strong consistency?
Date Sun, 06 Sep 2015 12:00:52 GMT
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
>

Mime
View raw message