I re-read my last post and didn't think I had done a good job articulating.
Sorry! I'll try again... 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 disable 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, and it's rather vital for that copy to make it over to keep the two datacenters in sync. Therefore I was wondering if Cassandra already intelligently special cases for HH-over-WAN (since this is common) even if HH is disabled or alternately if there's a way to enable HH for WAN replication only while disabling it for the LOCAL_QUORUM? Thank you. Thanks, Karthik On Tue, Jun 26, 2012 at 10:14 AM, Karthik N <karthik....@gmail.com> wrote: > 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 >> >>
