Procjena i planiranje kapaciteta — izračunavanje očekivanog opterećenja, količine podataka i potrebnih resursa — važan je dio dizajna sustava. Grube "procjene na leđima papira" informiraju dizajnerske odluke (koliko skalirati, koji resursi su potrebni) i često se pojavljuju u intervjuima za dizajn.
Zašto je procjena važna
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)
Što procjenjivati (procjena na leđima papira)
✓ 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
