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From Eric Plowe <>
Subject Re: ONE has much higher latency than LOCAL_ONE
Date Wed, 22 Mar 2017 00:23:34 GMT
ONE means at least one replica node to ack the write, but doesn't require
that the coordinator route the request to a node in the local data center.

LOCAL_ONE was introduced to handle the case of when you have multiple data
centers and cross data center traffic is not desirable.

In multiple datacenter clusters, a consistency level of ONE is often
desirable, but cross-DC traffic is not. LOCAL_ONEaccomplishes this. For
security and quality reasons, you can use this consistency level in an
offline datacenter to prevent automatic connection to online nodes in other
datacenters if an offline node goes down.




On Tue, Mar 21, 2017 at 7:49 PM Shannon Carey <> wrote:

> The cluster is in two DCs, and yes the client is deployed locally to each
> DC.
> From: Matija Gobec <>
> Reply-To: "" <>
> Date: Tuesday, March 21, 2017 at 2:56 PM
> To: "" <>
> Subject: Re: ONE has much higher latency than LOCAL_ONE
> Are you running a multi DC cluster? If yes do you have application in both
> data centers/regions ?
> On Tue, Mar 21, 2017 at 8:07 PM, Shannon Carey <> wrote:
> I am seeing unexpected behavior: consistency level ONE increases read
> latency 99th percentile to ~108ms (95th percentile to 5ms-90ms) up from
> ~5ms (99th percentile) when using LOCAL_ONE.
> I am using DSE 5.0 with Datastax client 3.0.0. The client is configured
> with a TokenAwarePolicy wrapping a DCAwareRoundRobinPolicy with
> usedHostsPerRemoteDc set to a very high number. Cassandra cluster has two
> datacenters.
> I would expect that when the cluster is operating normally (all local
> nodes reachable), ONE would behave the same as LOCAL_ONE. The  Does anyone
> know why this is not the case?

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