title: Cheatsheets description: Dense reference tables for the night before: latency numbers, selection matrices, consistency tables, the problem-to-pattern map, checklists and a glossary.
Cheatsheets¶
Dense, scannable tables for the night before and the minutes between rounds: the canonical latency and estimation numbers every page on this site uses, database and queue selection matrices, consistency and isolation tables, the problem-to-pattern map, round checklists, the clarifying-question bank and a glossary. They summarise; the linked pages explain. Keep the latency sheet open while you practise estimation until the orders of magnitude are automatic.
Tiers: P0 must be solid before any interview, P1 is expected of a strong SDE2, P2 is stretch material for when the rest is done.
Start here (P0)¶
- Latency numbers and estimation tables
- Database selection matrix
- Problem to pattern quick reference
- HLD round checklist
- LLD round checklist
All pages¶
| # | Page | Tier | Covers |
|---|---|---|---|
| 1 | Latency numbers and estimation tables | P0 | Latency ladder (ranges), powers of two, nines to downtime, QPS/storage/bandwidth formulas, per-node capacity rules of thumb, object sizes… |
| 2 | Database selection matrix | P0 | Rows: PostgreSQL/MySQL, DynamoDB, Cassandra, MongoDB, Redis, Elasticsearch, Neo4j, InfluxDB/Timescale, ClickHouse/BigQuery… |
| 3 | Queue and stream selection | P1 | Kafka, RabbitMQ, SQS/SNS, Pulsar, Redis Streams, Kinesis by ordering, delivery, retention and replay, throughput, fan-out, use when. |
| 4 | Consistency, replication and isolation tables | P1 | Replication topology by consistency, failover and conflicts; isolation levels by anomalies; N/W/R configurations and their guarantees… |
| 5 | Problem to pattern quick reference | P0 | Symptom to pattern to Pythonic idiom to example problem page; confusion pairs (Strategy/State/Template Method, Decorator/Proxy/Adapter… |
| 6 | HLD round checklist | P0 | Step-by-step with must-say phrases, required artifacts per step, red flags, ten deep-dive starters that work for any system. |
| 7 | LLD round checklist | P0 | Step-by-step, Amazon OOD rubric mapping, code-quality checklist (types, dataclasses, enums, exceptions, tests), when to stop adding… |
| 8 | Common SDE2 mistakes in design rounds | P1 | Twenty HLD and twenty LLD mistakes, each with symptom, why it costs, fix. |
| 9 | Clarifying-question bank | P1 | Grouped: users and actors, scale, read/write ratio, consistency, latency, durability, availability, geography, cost, security and privacy… |
| 10 | Glossary | P1 | At least 150 terms, one line each, each linked to the page that defines it. |
| 11 | Off-the-shelf building blocks | P1 | One-paragraph cards: Redis, Memcached, Kafka, RabbitMQ, Cassandra, DynamoDB, PostgreSQL, Elasticsearch, ZooKeeper/etcd, S3, CDN… |