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https://issues.apache.org/jira/browse/CASSANDRA-12104?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15362763#comment-15362763
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Thom Valley commented on CASSANDRA-12104:
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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
while
The bandwidth utilization between DCs dropped
> 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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