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From Jun Wu <wuxiaomi...@hotmail.com>
Subject RE: Question about replica and replication factor
Date Tue, 20 Sep 2016 04:50:09 GMT
Hi Ben,
    Thanks for the quick response. 
    It's clear about the example for single row/partition. However, normally data are not
single row. Then for this case, I'm still confused. http://docs.datastax.com/en/cassandra/2.1/cassandra/dml/architectureClientRequestsRead_c.html
    The link above gives an example of 10 nodes cluster with RF = 3. But the figure and the
words in the post shows that the coordinator only contact/read data from one replica, and
operate read repair for the left replicas. 
    Also, how could read accross all nodes in the cluster? 
    Thanks!
Jun


From: ben.slater@instaclustr.com
Date: Tue, 20 Sep 2016 04:18:59 +0000
Subject: Re: Question about replica and replication factor
To: user@cassandra.apache.org

Each individual read (where a read is a single row or single partition) will read from one
node (ignoring read repairs) as each partition will be contained entirely on a single node.
To read the full set of data,  reads would hit at least two nodes (in practice, reads would
likely end up being distributed across all the nodes in your cluster).
CheersBen
On Tue, 20 Sep 2016 at 14:09 Jun Wu <wuxiaomin98@hotmail.com> wrote:



Hi there,
    I have a question about the replica and replication factor. 
    For example, I have a cluster of 6 nodes in the same data center. Replication factor RF
is set to 3  and the consistency level is default 1. According to this calculator http://www.ecyrd.com/cassandracalculator/,
every node will store 50% of the data.
    When I want to read all data from the cluster, how many nodes should I read from, 2 or
1? Is it 2, because each node has half data? But in the calculator it show 1: You are really
reading from 1 node every time.
   Any suggestions? Thanks!
Jun 		 	   		  -- 
————————Ben SlaterChief Product OfficerInstaclustr: Cassandra + Spark - Managed
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