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Thom Valley commented on CASSANDRA-12104:
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Ariel,
Something to consider in that is both what Jeremiah stated above, but also the
fact that DC location can heavily impact both available bandwidth and latency.
In the example I have, there are two DCs in the US, relatively close to each
other (30ms apart) with almost 10G bandwidth between them, but the remote DCs
vary from 70ms up to over 200 ms with substantially less bandwidth available.
The ideal scenario for most inter-dc throttles would be to control it by
connection (by that I mean each distinct inter-dc path). But perhaps that is
too complicated.
I will get the details from the customer on exactly what levels showed the
benefits based on which DC we were evaluating.
> Handle coalesce efforts for inter-dc traffic discretely from intra-dc traffic
> -----------------------------------------------------------------------------
>
> Key: CASSANDRA-12104
> URL: https://issues.apache.org/jira/browse/CASSANDRA-12104
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Thom Valley
> Priority: Minor
>
> In relationship to CASSANDRA-8692, we have discovered that pushing coalescing
> windows to the point where they have a positive impact on inter-dc traffic
> overhead appears to have causes delays in intra-dc traffic (namely, quorum
> requests between nodes). Having the same coalescing strategy apply to all
> messages (especially intra-dc request/response messages) seems like a bad
> idea.
> This was in a 5 DC environment with from 30 to 130 ms of latency between the
> DCs. Local network was entirely unrestricted 10G ethernet.
> Being able to apply different coalescing rules to those two classifications
> of traffic would allow much more effective tuning of the coalescing
> strategies, save inter-dc bandwidth while not having any impact on intra-dc
> message handling.
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