Understand the problem and establish the design scope

There is no perfect design. Each design achieves a specific balance regarding the tradeoffs of read, write, and memory usage. Another tradeoff has to be made was between consistency and availability. In this chapter, we design a key-value store that comprises of the following characteristics:

• The size of a key-value pair is small: less than 10 KB.

• Ability to store big data.

• High availability: The system responds quickly, even during failures.

• High scalability: The system can be scaled to support large data sets.

• Automatic scaling: The addition/deletion of servers should be automatic based on traffic.

• Tunable consistency.

• Low latency.

Single server key-value store

Developing a key-value store that resides in a single server is easy. An intuitive approach is to store key-value pairs in a hash table, which keeps everything in memory. Even though memory access is fast, fitting everything in memory may be impossible due to the space constraint. Two optimizations can be done to fit more data in a single server:

• Data compression

• Store only frequently used data in memory and the rest on disk

Even with these optimizations, a single server can reach its capacity very quickly. A distributed key-value store is required to support big data.