Latency numbers every programmer should know

Source: Hacker News

Cache latencies

• L1 cache reference: 1 ns
• L2 cache reference: 4 ns
• Branch mispredict: 3 ns

Memory latency

• Main memory reference: 100 ns
• Read 1 000 000 bytes sequentially from memory: 741 ns

Disk / SSD latencies

• SSD sequential read: 12.245 µs
• SSD random read: 16.0 µs
• Read 1 000 000 bytes sequentially from SSD (disk): 358.968 µs
• Disk seek: 1.649 ms

Synchronization

• Mutex lock / unlock: 16 ns

Network latencies

• Send 2 000 bytes over a commodity network: 5 ns (per byte overhead)
• Round‑trip within the same datacenter: 500 µs
• Packet round‑trip (CA → Netherlands): 150 ms

References

• [github.com/chubin/late.nz] – MIT License
• Console port of “Jeff Dean’s latency numbers”
• Source: [github.com/colin-scott/interactive_latencies]