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From "stone (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-11569) Track message latency across DCs
Date Wed, 25 May 2016 01:15:13 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-11569?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15299277#comment-15299277
] 

stone commented on CASSANDRA-11569:
-----------------------------------

I konw that,what I confuse about is how to deal with the async write request.i.e

I have two datacenters,call source dc,dst dc.the CL is LOCAL_QUORUM,and each dc has 3 replicator.
I run a long continue write workload on source dc,and if the latency between dc is low,there
is no problem,
but when the latency  is high,async write request need more time than usual,so some requests
need to wait in the queue.

what I want to know,when the async request time is too long,will the source dc think the node
is down,and give up the request,then write hinted off like the dst node really down.
I mean in dst dc,some of the async request will success,and some of the async request will
fail.

> Track message latency across DCs
> --------------------------------
>
>                 Key: CASSANDRA-11569
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11569
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Observability
>            Reporter: Chris Lohfink
>            Assignee: Chris Lohfink
>            Priority: Minor
>         Attachments: CASSANDRA-11569.patch, CASSANDRA-11569v2.txt, nodeLatency.PNG
>
>
> Since we have the timestamp a message is created and when arrives, we can get an approximate
time it took relatively easy and would remove necessity for more complex hacks to determine
latency between DCs.
> Although is not going to be very meaningful when ntp is not setup, it is pretty common
to have NTP setup and even with clock drift nothing is really hurt except the metric becoming
whacky.



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