System Design Simulator

2026 EDITION
Preset Scenarios:
Scale Controls Twitter Feed
Daily Active Users (DAU) 100M
Read : Write Ratio 100 : 1
Avg Payload Size 500 Bytes
Cache Hit Ratio 85.0%
Fanout Factor (Reads/Write) 200
DB Shards 8 Shards
Topology Topology Canvas (Drag to reposition) Particle Traffic: Active
Capacity Telemetry
● HEALTHY
Peak Read / Write QPS
231,481 / 2,315
Read Peak (2.0x avg) | Fanout multiplier applied
Estimated SLA p99 Latency
18.4 ms
Cache lookup (2ms) + DB Shard lookup (12ms)
RAM Required (Cache Tier)
120.0 GB
20% active working set stored in Redis
Storage Ingest / Annual Growth
100.0 GB/day | 36.5 TB/yr
Raw storage excluding replication factor
Active Design Formulas
• QPS = (DAU × Actions) / 86,400
• Peak QPS = Avg QPS × 2.0
• Latency = (Hit% × L_cache) + ((1-Hit%) × L_db)
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