HLDsystem_design~12 mins

Cache eviction policies (LRU, LFU, TTL) in HLD - Architecture Diagram

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System Overview - Cache eviction policies (LRU, LFU, TTL)

This system manages a cache to speed up data access by storing frequently used data temporarily. It uses eviction policies like LRU (Least Recently Used), LFU (Least Frequently Used), and TTL (Time To Live) to decide which data to remove when the cache is full or data expires.

Architecture Diagram

User
  |
  v
Load Balancer
  |
  v
API Gateway
  |
  v
Cache Manager
 /   |    \
LRU  LFU   TTL
  \   |    /
   Cache Storage
      |
      v
  Database

Components

User

client

Sends requests to access data

Load Balancer

load_balancer

Distributes incoming requests evenly to API Gateway

API Gateway

api_gateway

Receives requests and routes them to Cache Manager

Cache Manager

service

Handles cache logic and applies eviction policies

LRU

eviction_policy

Evicts least recently used items when cache is full

LFU

eviction_policy

Evicts least frequently used items when cache is full

TTL

eviction_policy

Evicts items after their time to live expires

Cache Storage

cache

Stores cached data for fast access

Database

database

Stores the original persistent data

Request Flow - 11 Hops

User → Load Balancer

Load Balancer → API Gateway

API Gateway → Cache Manager

Cache Manager → Cache Storage

Cache Storage → Cache Manager

Cache Manager → Database

Database → Cache Manager

Cache Manager → Cache Storage

Cache Manager → API Gateway

API Gateway → Load Balancer

Load Balancer → User

Failure Scenario

Component Fails:Cache Storage

Impact:Cache misses increase, causing more direct database queries and higher latency

Mitigation:System continues to serve data from database; cache rebuilds as data is requested; consider cache replication or fallback cache

Architecture Quiz - 3 Questions

Test your understanding

Which eviction policy removes the data that was used least recently?

ALFU

BLRU

CTTL

DRandom Eviction

Design Principle

This design shows how different cache eviction policies help manage limited cache space by removing data based on usage patterns or expiration time, improving system performance and resource use.