System Design Cheat Sheet =link= ✰ [COMPLETE]

Ordering, at-least-once vs exactly-once, dead-letter queues, backpressure. 6. Consistency & Replication | Model | Behavior | Latency | Data loss risk | |-------|----------|---------|----------------| | Strong | All reads see latest write | Higher | None (if quorum) | | Eventual | Reads may be stale, converge over time | Lower | Possible during failover | | Read-your-writes | Session sees own writes | Medium | None | | Monotonic reads | Reads never go back in time | Medium | None |

LRU, LFU, TTL, FIFO.

Start with relational. Scale with read replicas → cache → sharding → NoSQL when needed. 4. Caching Strategies | Strategy | How it works | Best for | |----------|-------------|-----------| | Cache-aside | App checks cache → misses DB → writes cache | Read-heavy workloads | | Read-through | Cache sits in front of DB | Consistent data, complex queries | | Write-through | Write to cache + DB synchronously | Write-heavy, need consistency | | Write-behind | Write to cache → async write to DB | High write throughput, eventual consistency | | Refresh-ahead | Cache auto-refreshes near-expiry data | Predictable access patterns | system design cheat sheet