Topic map.
Every topic and what it connects to. Data structures on the left feed the system designs that depend on them, and those show up in the production notes. Hover or focus a topic to light up its connections.
Data structures & algorithms
- Big-O How to read time and space complexity, from counting loop steps to amortized analysis, query plans and N+1 bugs, with demos and production code.
Connects toDSAHeapsDSABinary searchDSAHash mapsDSASliding windowDSATwo pointers
- Hash maps How hash maps and sets work, from a coat check to CPython's dict, Swiss tables and hash flooding, with demos, exercises and real production code.
Connects toDSABig-OSystem designConsistent hashingSystem designCachingSystem designIdempotencySystem designRate limiterDSASliding windowDSATwo pointers
- Two pointers How two pointers work, from reversing a string to Floyd's cycle detection, PostgreSQL merge joins and one-pass sync diffs, with demos and exercises.
Connects toDSABig-ODSAHash mapsDSASliding window
- Sliding window How the sliding window technique works, from a running sum to monotonic deques, stream windows and TCP, with step-through demos and real production code.
Connects toDSABig-ODSATwo pointersDSAHash mapsDSAHeapsSystem designRate limiter
- Binary search How binary search works, from a guessing game to bisect, answer-space search, cache-friendly layouts, B-tree indexes and git bisect, with demos.
Connects toDSABig-OSystem designConsistent hashing
- Heaps How heaps and priority queues work, from ER triage to heapq, heapify, Dijkstra, timing wheels and the asyncio scheduler, with demos and production code.
Connects toDSABig-OSystem designQueuesDSASliding window
System design
- Rate limiter How rate limiters work, from a ten-line counter to a distributed Redis design: five algorithms, a live simulator, two classic bugs and real production code.
Connects toDSAHash mapsDSASliding windowSystem designReal-time chatSystem designQueuesProductionCongestive collapse
- Idempotency Why retries double-charge and how to stop it: idempotency keys, upserts, backoff with jitter, the outbox and inbox, with live demos and real production code.
Connects toDSAHash mapsSystem designReal-time chatSystem designQueuesProductionNo lost turns
- Caching How caching works, from TTLs and cache-aside to eviction, HTTP headers, stampedes and LLM caches, with two live simulators and real production code.
Connects toDSAHash mapsSystem designConsistent hashing
- Queues How job queues work, from one producer and one worker to Little's Law, Celery tuning, retry storms and backpressure, with two live simulators and real code.
Connects toSystem designRate limiterSystem designIdempotencyDSAHeapsSystem designReal-time chatProductionCongestive collapse
- Consistent hashing How consistent hashing works, from hash % N to rings, virtual nodes, jump hash, Maglev and Redis Cluster slots, with live demos and measured numbers.
Connects toSystem designCachingDSAHash mapsDSABinary searchSystem designReal-time chat
- Real-time chat How real-time chat works: polling vs WebSockets, message ordering, receipts, presence, fan-out across servers and slow readers, with live demos and real code.
Connects toSystem designIdempotencySystem designRate limiterSystem designQueuesSystem designConsistent hashing
Production notes
- Congestive collapse Throughput fell from 157.6 to 55 req/s as load rose, with zero errors. How a latency-derived concurrency limit fixed it, and where it stops helping.
Connects toSystem designRate limiterSystem designQueues
- No lost turns Queues lose tasks and deploys kill workers. How an owed-reply marker, a 60-second sweeper and a sent marker make sure every customer gets an answer.
Connects toSystem designIdempotency
- Pin your model IDs A vendor moved a model alias and every AI feature changed model and price with no deploy. What we pin now, and why failover skips vendors without keys.