Let me attempt to articulate my question a little better. Say I choose LOCAL_QUORUM with a Replication Factor of 3. Cassandra stores three copies in my local datacenter. Therefore the cost associated with "losing" one node is not very high locally, and I usually HH, and use read repair/nodetool repair instead.
However over the WAN network blips are quite normal and HH really helps. More so because for WAN replication Cassandra sends only one copy to a coordinator in the remote datacenter. Therefore I was wondering if Cassandra already intelligently optimizes for HH-over-WAN (since this is common) or alternately if there's a way to enable HH for WAN replication? Thank you. On Tue, Jun 26, 2012 at 9:22 AM, Mohit Anchlia <mohitanch...@gmail.com> wrote: > > > On Tue, Jun 26, 2012 at 8:16 AM, Karthik N <karthik....@gmail.com> wrote: >> >> Since Cassandra optimizes and sends only one copy over the WAN, can I opt >> in only for HH for WAN replication and avoid HH for the local quorum? (since >> I know I have more copies) >> >> > > I am not sure if I understand your question. In general I don't think you > can selectively decide on HH. Besides HH should only be used when the outage > is in mts, for longer outages using HH would only create memory pressure. >> >> On Tuesday, June 26, 2012, Mohit Anchlia wrote: >>> >>> >>> On Tue, Jun 26, 2012 at 7:52 AM, Karthik N <karthik....@gmail.com> wrote: >>>> >>>> My Cassandra ring spans two DCs. I use local quorum with replication >>>> factor=3. I do a write in DC1 with local quorum. Data gets written to >>>> multiple nodes in DC1. For the same write to propagate to DC2 only one >>>> copy is sent from the coordinator node in DC1 to a coordinator node in >>>> DC2 for optimizing traffic over the WAN (from what I have read in the >>>> Cassandra documentation) >>>> >>>> Will a Wan hiccup result in a Hinted Handoff (HH) being created in >>>> DC1's coordinator for DC2 to be delivered when the Wan link is up >>>> again? >>> >>> >>> I have seen hinted handoff messages in the log files when the remote DC >>> is unreachable. But this mechanism is only used for a the time defined in >>> cassandra.yaml file. >> >> >> >> -- >> Thanks, Karthik > >
