Interestingly, Amazon took a different view with Dynamo. They decided that availability was massively important, as latency had a significant impact on the success of their business applications. Amazon’s web applications are built from a chain of services - the web page that you see at amazon.com is built by a large number of separate services, all executing in parallel. The speed with which those services can render your page directly affects your happiness with the web-site, and consequentially the likelihood of you buying that toaster oven. Therefore each service is committed to a Service-Level Agreement (SLA) that stipulates a performance contract which each service guarantees adherence to. These SLAs at Amazon are expressed as 99.9th percentile guarantees, that is that 99.9% of the calls to that service will meet the SLA requirements. Interestingly enough, this explains why some of the myriad widgets that now litter any product page at Amazon sometimes simply do not appear - if they break the SLA the web server goes ahead and sends the page without them in order not to compromise latency to the user. Clearly, at Amazon, responsiveness is king.
