Estimering og kapacitetsplanlægning — beregning af forventet belastning, datamængde og ressourcebehov — er en vigtig del af systemdesign. Rå "tilbage-på-konvolutten" beregninger informerer designbeslutninger (hvor meget man skal skalere, hvilke ressourcer der er behov for) og er almindelige i designinterviews.
Hvorfor estimering betyder noget
Estimating scale informs DESIGN decisions:
→ how many servers? how much storage? what database? do you need sharding/caching?
→ understanding the SCALE (small vs massive) shapes the whole design
→ rough numbers guide whether/how to scale (don't over- or under-engineer)
Hvad skal estimeres (tilbage-på-konvolutten)
✓ TRAFFIC → users, requests/sec (QPS); read vs write ratio (e.g. 100:1 reads:writes)
→ peak vs average (design for peak); daily active users → requests
✓ STORAGE → data size per item × volume × growth over time → total storage (and growth rate)
✓ BANDWIDTH → data transferred per second (request size × QPS)
✓ MEMORY → cache size needed (e.g. cache the hot 20% of data)
→ rough estimates (order of magnitude) → good enough to inform design
