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
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