Short answer: If time elapsed > max_hint_window_in_ms then hints will stop being created. You will need to rely on your read consistency level, read repair and anti-entropy repair operations to restore consistency.
Long answer: http://www.slideshare.net/jasedbrown/understanding-antientropy-in-cassandra Ben Bromhead Instaclustr | www.instaclustr.com | @instaclustr | +61 415 936 359 On 30 May 2014, at 8:40 am, Tupshin Harper <tups...@tupshin.com> wrote: > When one node or DC is down, coordinator nodes being written through will > notice this fact and store hints (hinted handoff is the mechanism), and > those hints are used to send the data that was not able to be replicated > initially. > > http://www.datastax.com/dev/blog/modern-hinted-handoff > > -Tupshin > > On May 29, 2014 6:22 PM, "Vasileios Vlachos" <vasileiosvlac...@gmail.com> > wrote: > Hello All, > > We have plans to add a second DC to our live Cassandra environment. Currently > RF=3 and we read and write at QUORUM. After adding DC2 we are going to be > reading and writing at LOCAL_QUORUM. > > If my understanding is correct, when a client sends a write request, if the > consistency level is satisfied on DC1 (that is RF/2+1), success is returned > to the client and DC2 will eventually get the data as well. The assumption > behind this is that the the client always connects to DC1 for reads and > writes and given that there is a site-to-site VPN between DC1 and DC2. > Therefore, DC1 will almost always return success before DC2 (actually I don't > know if it is possible for DC2 to be more up-to-date than DC1 with this > setup...). > > Now imagine DC1 looses connectivity and the client fails over to DC2. > Everything should work fine after that, with the only difference that DC2 > will be now handling the requests directly from the client. After some time, > say after max_hint_window_in_ms, DC1 comes back up. My question is how do I > bring DC1 up to speed with DC2 which is now more up-to-date? Will that > require a nodetool repair on DC1 nodes? Also, what is the answer when the > outage is < max_hint_window_in_ms instead? > > Thanks in advance! > > Vasilis > -- > Kind Regards, > > Vasileios Vlachos
