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Date: Fri, 27 Jul 2012 13:43:07 -0500 (CDT)
Subject: Re: increased RF and repair, not working?
From: "Dave Brosius" <dbrosius@mebigfatguy.com>
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You have RF=2, CL= Quorum but 3 nodes. So each row is represented on 2 of the 3 nodes.If you take a node down, one of two things can happen when you attempt to read a row.The row lives on the two nodes that are still up. In this case you will successfully read the data.The row lives on one node that is up, and one node that is down. In this case the read will fail because you haven't fulfilled the quorum (2 nodes in agreement) requirement.   ----- Original Message -----From: &quot;Riyad Kalla&quot; >;rkalla@gmail.com 
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You have RF=2, CL= Quorum but 3 nodes.&nbsp;<br /><br />So each row is represented on 2 of the 3 nodes.<br /><br />If you take a node down, one of two things can happen when you attempt to read a row.<br /><br />The row lives on the two nodes that are still up. In this case you will successfully read the data.<br /><br />The row lives on one node that is up, and one node that is down. In this case the read will fail because you haven't fulfilled the quorum (2 nodes in agreement) requirement.<br /> <br /> <br /> <!--replyfwdwrap--><div style="background-image: url(http://webmail.mailanyone.net/de/r_bg_img.gif);background-position:top;background-repeat:repeat-x;"><strong>----- Original Message -----</strong><br /><strong>From:</strong> &quot;Riyad Kalla&quot; &lt;rkalla@gmail.com&gt; <br /><strong>Sent:</strong> Fri, July 27, 2012 8:08<br /><strong>Subject:</strong> Re: increased RF and repair, not working?<br /><br /><table width="100%" cellspacing="5"><tbody><tr><td><div class="Priva
 teMsgDiv"><!-- begin sanitized html --> Dave, per my understanding of Yan's description he has 3 nodes and took one down manually to test; that should have worked, no?<br /><br /><div class="gmail_quote">On Thu, Jul 26, 2012 at 11:00 PM, Dave Brosius <span dir="ltr">&lt;<a href="mailto:dbrosius@mebigfatguy.com" target="_new">dbrosius@mebigfatguy.com</a>&gt;</span> wrote:<br />  <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">              <div bgcolor="#FFFFFF" text="#000000">Quorum is defined as<br />          <pre style="line-height:normal;text-indent:0px;letter-spacing:normal;font-variant:normal;text-transform:none;font-style:normal;font-size:13px;font-weight:normal;word-spacing:0px"><big><span>(</span><span>replication_factor</span> <span>/</span> <span>2</span><span>)</span> <span>+</span> <span>1</span></big>

<big>therefore quorum when rf = 2 is 2! so in your case, both nodes must be up.  Really, using Quorum only starts making sense as a 'quorum' when RF=3 </big></pre><div><div class="h5"><span><br />       <br />     </span><br />     <br />     <br />     On 07/26/2012 10:38 PM, Yan Chunlu wrote:     <blockquote type="cite">I am using Cassandra 1.0.2, have a 3 nodes cluster.       the consistency level of read &amp; write are &nbsp;both QUORUM.       <div>&nbsp;</div>       <div>At first the RF=1, and I figured that one node down will         cause the cluster unusable. so I changed RF to 2, and run         nodetool repair on every node(actually I did it twice). &nbsp;</div>       <div>&nbsp;</div>       <div>After the operation I think my data should be in at least two         nodes, and it would be okay if one of them is down.</div>       <div>&nbsp;</div>       <div>But when I tried to simulate the failure, by disablegossip of         one node, and the cluster knows this node is dow
 n. then access         data from the cluster, it returned         &nbsp;&quot;MaximumRetryException&quot;(pycassa). &nbsp; as my experiences this is         caused by &quot;UnavailableException&quot;, which is means the data it is         requesting is on a node which is down.</div>       <div>&nbsp;</div>       <div>so I wonder my data might not be replicated right, what         should I do? thanks for the help!<br />         <div>&nbsp;</div>         <div>here is the keyspace info:</div>         <div>&nbsp;</div>         <div><i><br />           </i></div>         <div><div><i>Keyspace: comments:</i></div>           <div><i>&nbsp; Replication Strategy:               org.apache.cassandra.locator.SimpleStrategy</i></div>           <div><i>&nbsp; Durable Writes: true</i></div>           <div><i>&nbsp; &nbsp; Options: [replication_factor:2]</i></div></div>         <div>&nbsp;</div>         <div>&nbsp;</div>         <div>&nbsp;</div>         <div>the scheme version is okay:</div>      
    <div>&nbsp;</div>         <div><div><i>[default@unknown] describe cluster;</i></div>           <div><i>Cluster Information:</i></div>           <div><i>&nbsp; &nbsp;Snitch: org.apache.cassandra.locator.SimpleSnitch</i></div>           <div><i>&nbsp; &nbsp;Partitioner:               org.apache.cassandra.dht.RandomPartitioner</i></div>           <div><i>&nbsp; &nbsp;Schema versions:&nbsp;</i></div>           <div><i><span style="white-space:pre-wrap">               </span>f67d0d50-b923-11e1-0000-4f7cf9240aef:               [192.168.1.129, 192.168.1.40, 192.168.1.50]</i></div></div>         <div>&nbsp;</div>         <div>&nbsp;</div>         <div>&nbsp;</div>         <div>the loads are as below:</div>         <div>&nbsp;</div>         <div><div><i>nodetool -h localhost ring</i></div>           <div><i>Address &nbsp; &nbsp; &nbsp; &nbsp; DC &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;Rack &nbsp; &nbsp; &nbsp; &nbsp;Status State &nbsp;               Load &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp
 ;Owns &nbsp; &nbsp;Token &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;               &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;</i></div>           <div><i>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;               &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;               &nbsp;113427455640312821154458202477256070484 &nbsp; &nbsp;&nbsp;</i></div>           <div><i>192.168.1.50 &nbsp; &nbsp;datacenter1 rack1 &nbsp; &nbsp; &nbsp; Up &nbsp; &nbsp; Normal               &nbsp;28.77 GB &nbsp; &nbsp; &nbsp; &nbsp;33.33% &nbsp;0 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;               &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;</i></div>           <div><i>192.168.1.40 &nbsp; &nbsp;datacenter1 rac
 k1 &nbsp; &nbsp; &nbsp; Up &nbsp; &nbsp; Normal               &nbsp;26.67 GB &nbsp; &nbsp; &nbsp; &nbsp;33.33%               &nbsp;56713727820156410577229101238628035242 &nbsp; &nbsp; &nbsp;</i></div>           <div><i>192.168.1.129 &nbsp; datacenter1 rack1 &nbsp; &nbsp; &nbsp; Up &nbsp; &nbsp; Normal               &nbsp;33.25 GB &nbsp; &nbsp; &nbsp; &nbsp;33.33%               &nbsp;113427455640312821154458202477256070484 &nbsp; &nbsp;</i></div></div></div>     </blockquote>     </div></div></div>  </blockquote></div><br /> <!-- end sanitized html --></div></td></tr> </tbody></table></div>
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