DynamoDB: An Inside Look Into NoSQL – Part 3

This is a guest post from 47Line Technologies.
In Part 2, we looked at Design Considerations of NoSQL and introduced the concept of eventual consistency. In this article, we will introduce the concepts and techniques used while architecting a NoSQL system.
The core distributed systems techniques employed in DynamoDB are – partitioning, replication, versioning, membership, failure handling and scaling. Phew! Did you really think that the internals will be simple? 🙂
DynamoDB Internals
The following table summarizes the list of techniques used in DynamoDB:

ProblemTechniqueAdvantage
PartioningConsistent HashingIncremental Scalability
High Availability for WritesVector Clocks with reconciliation during readsVersion size is decoupled from update rates
Handling temporary failuresSloppy Quorum and Hinted HandoffProvides high availability & durability guarantee when some replicas are not available
Recovery from permanent failuresAnti-entropy using Merkle treesSynchronizes divergent replicas in the background
Membership & Failure DetectionGossip-based membership protocol & failure detectionPreserves symmetry and avoids having a centralized registry for storing membership and node liveness information

I know I have covered a lot of lingo and buzz words. If you really need to take a deep breath, now is the time! Fear not, in subsequent articles we will deep-dive into each of the above mentioned techniques. Remember, the devil is in the details!

System Interface

DynamoDB exposes two interfaces: get and put. The get(key) operation locates the object associated with the key and returns it along with a context. The put(key, context, object) operation uses key to determine the associated replicas and writes the object in those replicas. The context information is invisible to the user and contains metadata such as version. DynamoDB applies an MD5 hash on the key to generate a 128-bit identifier, which is used to determine the replicas that are responsible for serving the key.
Article authored by Vijay Olety

Written by

47Line is building solutions solving critical business problems using “cloud as the backbone”. The team has been working in Cloud Computing domain for last 6 years and have proven thought leadership in Cloud, Big Data technologies.

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