Evaluation of a Distributed Cache's Design

Evaluate the cache on the complete request path and under the failures it must tolerate. Local data-structure complexity is only one part of latency; network time, miss handling, and contention also matter.

Requirements compliance

Let’s evaluate the design against our requirements.

High performance

The following design choices contribute to high performance:

• A binary search over a sorted consistent-hash ring takes $\text{O(log N)}$ time, where $\text{N}$ counts ring positions. With one position per shard, it is the shard count; virtual nodes add positions. Other lookup representations can have different costs.

• Hash tables provide expected constant-time lookup, subject to hashing and collision behavior.

• A doubly linked list supports constant-time LRU pointer updates once the entry is located, but concurrent access can contend on shared state.

• Transport, serialization, queueing, and payload size contribute to remote-call latency. TCP or UDP alone does not guarantee speed.

• Read replicas can distribute eligible reads within their combined capacity.

• RAM avoids a local disk read, but does not eliminate the other costs on a cache hit.