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Design SQL backed KV Store

Problem Statement

Design a KV Store built on top of a SQL (relational) database. The store exposes APIs to GET, PUT, DEL keys. Along with these core functiona, there should be an API to set TTL to an existing key, post which the key is auto-deleted from the store. Scale this KV store 1 million concurrent API calls and a total storage of 5000 TB.

Relog - SQL Backed KV Store

Requirements

The problem statement is something to start with, be creative and dive into the product details and add constraints and features you think would be important.

Core Requirements

  • should be able to GET, PUT, DEL, TTL on keys
  • upon expiration the key should be auto-deleted
  • should handle 1 million concurrent transactions
  • max storage of one KV store would be 5000 TB

High Level Requirements

  • make your high-level components operate with high availability
  • ensure that the data in your system is durable, not matter what happens
  • define how your system would behave while scaling-up and scaling-down
  • make your system cost-effective and provide a justification for the same
  • describe how capacity planning helped you made a good design decision
  • think about how other services will interact with your service

Micro Requirements

  • ensure the data in your system is never going in an inconsistent state
  • ensure your system is free of deadlocks (if applicable)
  • ensure that the throughput of your system is not affected by locking, if it does, state how it would affect

Output

Design Document

Create a design document of this system/feature stating all critical design decisions, tradeoffs, components, services, and communications. Also specify how your system handles at scale, and what will eventually become a chokepoint.

Do not create unnecessary components, just to make design look complicated. A good design is always simple and elegant. A good way to think about it is if you were to create a spearate process/machine/infra for each component and you will have to code it yourself, would you still do it?

Prototype

To understand the nuances and internals of this system, build a prototype that

  • expose GET, PUT, DEL, TTL over HTTP server
  • simulate concurrent transactions and measure the throughput

Recommended Tech Stack

This is a recommended tech-stack for building this prototype

Which Options
Language Golang, Java, C++
Database Relational Database - MySQL

Keep in mind

These are the common pitfalls that you should keep in mind while you are building this prototype

  • have a primary key to your tables otherwise the entire table might get locked
  • auto-deletion of keys at scale is tricky, think about it well

Outcome

You'll learn

  • SQL Transactions
  • Database Locking
  • Scaling by sharding

Share and shoutout

If you find this assignment helpful, please

  • share this assignment with your friends and peers
  • star this repository and help it reach a wider audience
  • give me a shoutout on Twitter @arpit_bhayani, or on LinkedIn at @arpitbhayani.

This assignment is part of Arpit's System Design Masterclass - A masterclass that helps you become great at designing scalable, fault-tolerant, and highly available systems.