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In previous post Distributed NoSQL: HBase and Accumulo, we explored two BigTable-like open source solutions. In this post we will learn about Riak, a highly available key-value store modeled after Amazon.com’s Dynamo. As we know, HBase and Accumulo provide strong consistency as a region/tablet is served by only one RegionServer/TabletServer at a time. However, this also introduces the availability problem. If a RegionServer fails, the corresponding regions will not be available during detection and recovery period. In contrast, Dynamo and Riak were designed to provide an “always-on” experience while sacrificing consistency under certain scenarios. Actually, the famous CAP theorem tells us that it is impossible for a distributed computer system to simultaneously provide all three of the following guarantees: Continue reading