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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Lendro Reox asked:<o:p></o:p></span></p>
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<span style="color:#1F497D">> </span>We're replicating our datacenter in another location (something like Amazons east and west coast) , thinking about our applications and<span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">>
</span>our use of Swift, is there any way that we can set up weights for our datanodes so if a request enter via for example DATACENTER 1 ,<span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">>
</span> then we want the main copy of the data being written on a datanode on the SAME datacenter o read from the same datacenter, so<span style="color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">>
</span>when we want to read it and comes from a proxy node of the same datacenter we dont add delay of the latency between the two datacenters. <br>
<span style="color:#1F497D">> </span>The moto is "if a request to write or read enters via DATACENTER 1 then is served via proxynodes/datanodes located on DATACENTER 1",<span style="color:#1F497D"><br>
> </span>then the replicas gets copied across zones over both datacenters.<o:p></o:p></p>
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<p class="MsoNormal"><span style="color:#1F497D">> </span>Routing the request to especific proxy nodes is easy, but dont know if swift has a way to manage this internally too for the datanodes <o:p></o:p></p>
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<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I don’t see how you would accomplish that with the current Swift infrastructure.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">An object is hashed to a partition, and the ring determines where replicas of that partition are stored.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">What you seem to be suggesting is that when an object is created in region X that it should be assigned to partition that is primarily stored in region X,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">While if the same object had been created in region Y it would be assigned to a partition that is primary stored in region Y.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The problem is that “where this object was first created” is not a contributor to the hash algorithm, nor could it be since there is no way for someone<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">trying to get that object to know where it was first created.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">What I think you are looking for is a solution where you have *<b>two</b>* rings, DATACENTER-WEST and DATACENTER-EAST. Both of these rings would have<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">an adequate number of replicas to function independently, but would asynchronously update each other to provide eventual consistency.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">That would use more disk space, but avoids making all updates wait for the data to be updated at each site.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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