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From "Thom Valley (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-12104) Handle coalesce efforts for inter-dc traffic discretely from intra-dc traffic
Date Tue, 05 Jul 2016 16:53:10 GMT


Thom Valley commented on CASSANDRA-12104:

We saw a marked though small reduction in inter-dc traffic.

Moving the window size large enough to see that reduction though resulted in increased request
latency at the coordinator level (due to quorum requests taking longer we believe).  

The application saw an increase in average request latency
The bandwidth utilization between DCs dropped

> Handle coalesce efforts for inter-dc traffic discretely from intra-dc traffic
> -----------------------------------------------------------------------------
>                 Key: CASSANDRA-12104
>                 URL:
>             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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