Oh, duh. Revise that. I was forgetting that multi-dc writes are sent to a single node in the other dc and tagged to be forwarded to other nodes within the dc.
So your quick-and-dirty estimate would be more like (write volume) x 2 to leave headroom for random other mechanics. R On 1/15/20, 11:07 AM, "Reid Pinchback" <rpinchb...@tripadvisor.com> wrote: Message from External Sender I would think that it would be largely driven by the replication factor. It isn't that the sstables are forklifted from one dc to another, it's just that the writes being made to the memtables are also shipped around by the coordinator nodes as the writes happen. Operations at the sstable level, like compactions, are local to the node. One potential wrinkle that I'm unclear on, is related to repairs. I don't know if merkle trees are biased to mostly bounce around only intra-dc, versus how often they are communicated inter-dc. Note that even queries can trigger some degree of repair traffic if you have a usage pattern of trying to read data recently written, because at the bleeding edge of the recent changes you'll have more cases of rows not having had time to settle to a consistent state. If you want a quick-and-dirty heuristic, I'd probably take (write volume) x (replication factor) x 2 as a guestimate so you have some headroom for C* and TCP mechanics, but then monitor to see what your real use is. R On 1/15/20, 4:14 AM, "Osman Yozgatlıoğlu" <osman.yozgatlio...@gmail.com> wrote: Message from External Sender Hello, Is there any way to calculate inter dc bandwidth requirements for proper operation? I can't find any info about this subject. Can we say, how much sstable collected at one dc has to be transferred to other? I can calculate bandwidth with generated sstable then. I have twcs with one hour window. Regards, Osman --------------------------------------------------------------------- To unsubscribe, e-mail: user-unsubscr...@cassandra.apache.org For additional commands, e-mail: user-h...@cassandra.apache.org