Week 10 — HLD Building Blocks & Graphs

intermediate hld dbms dsa

Goal: Learn the infrastructure building blocks that every system design answer needs, pair it with NoSQL knowledge, and start conquering graph algorithms.

Topics

DayFocusTopics
MonHLD NetworkingDNS and How the Internet Works · Load Balancers · Proxies and Reverse Proxies
TueHLD Caching & CDNCaching · Content Delivery Networks · Message Queues
WedDBMS NoSQLDocument Stores · Key-Value Stores
ThuDBMS Data ModelingNoSQL Data Modeling · Choosing the Right Database
FriDSA GraphsTries · Graph Representations · BFS and DFS

Key Concepts

  • L4 vs L7 load balancing — when you need protocol awareness and when raw throughput wins
  • Cache invalidation strategies — write-through, write-behind, and cache-aside patterns
  • Pub/sub vs message queue — fan-out vs exactly-once processing, and when to use each
  • When to use MongoDB vs Redis vs PostgreSQL — there’s no universal answer, only tradeoffs
  • Adjacency list vs adjacency matrix — space/time tradeoffs for sparse vs dense graphs
  • BFS for shortest path (unweighted) vs DFS for exploration and cycle detection

Practice

  • Draw the architecture of any website you use daily — identify the LB, cache, CDN, and queue layers
  • Pick 3 real apps and justify which database type (document, key-value, relational) fits best
  • Implement BFS and DFS on a graph — both iterative and recursive
  • Build a Trie and implement autocomplete search

~13 topics · ~1.5-2 hrs/day · Focus: read the linked notes, then code each concept