If you require the best precision you can get, setting up a pair of stratum 1 ntpd masters in each data center location with a GPS modules is not terribly complex. Low latency and jitter on servers you manage. 140ms is a long way away network-wise, and I would suggest that was a poor choice of upstream (probably stratum 2 or 3) source.
As Jonathan mentioned, there's no guarantee from Cassandra, but if you need as close as you can get, you'll probably need to do it yourself. (I run several stratum 2 ntpd servers for pool.ntp.org) -- Kind regards, Michael On 02/09/2017 06:47 PM, Kant Kodali wrote: > Hi Justin, > > There are bunch of issues w.r.t to synchronization of clocks when we > used ntpd. Also the time it took to sync the clocks was approx 140ms > (don't quote me on it though because it is reported by our devops :) > > we have multiple clients (for example bunch of micro services are > reading from Cassandra) I am not sure how one can achieve > Linearizability by setting timestamps on the clients ? since there is no > total ordering across multiple clients. > > Thanks! > > > On Thu, Feb 9, 2017 at 4:16 PM, Justin Cameron <jus...@instaclustr.com > <mailto:jus...@instaclustr.com>> wrote: > > Hi Kant, > > Clock synchronization is important - you should ensure that ntpd is > properly configured on all nodes. If your particular use case is > especially sensitive to out-of-order mutations it is possible to set > timestamps on the client side using the > drivers. > https://docs.datastax.com/en/developer/java-driver/3.1/manual/query_timestamps/ > > <https://docs.datastax.com/en/developer/java-driver/3.1/manual/query_timestamps/> > > We use our own NTP cluster to reduce clock drift as much as > possible, but public NTP servers are good enough for most > uses. > https://www.instaclustr.com/blog/2015/11/05/apache-cassandra-synchronization/ > > <https://www.instaclustr.com/blog/2015/11/05/apache-cassandra-synchronization/> > > Cheers, > Justin > > On Thu, 9 Feb 2017 at 16:09 Kant Kodali <k...@peernova.com > <mailto:k...@peernova.com>> wrote: > > How does Cassandra achieve Linearizability with “Last write > wins” (conflict resolution methods based on time-of-day clocks) ? > > Relying on synchronized clocks are almost certainly > non-linearizable, because clock timestamps cannot be guaranteed > to be consistent with actual event ordering due to clock skew. > isn't it? > > Thanks! > > -- > > Justin Cameron > > Senior Software Engineer | Instaclustr > > > > > This email has been sent on behalf of Instaclustr Pty Ltd > (Australia) and Instaclustr Inc (USA). > > This email and any attachments may contain confidential and legally > privileged information. If you are not the intended recipient, do > not copy or disclose its content, but please reply to this email > immediately and highlight the error to the sender and then > immediately delete the message. > >
