延迟数
| type | range | for |
|---|---|---|
| 即时响应 | < 100ms | 搜索自动补全、按钮点击 |
| 流畅响应 | 100ms - 300ms | 拖拽、滚动、页面、内容加载 |
| 可接受响应 | 300ms - 1000ms | 交互式应用、提交表单 |
| 过长响应 | > 1000ms | 用户会感到延迟 |
| VoIP | 150ms - 300ms | 语音通话 |
Latency Comparison Numbers ~ 2012
- Interactive Latency Numbers Every Programmer Should Know
- HN
- Gist Neo
- Grace Hopper explains Nanoseconds
- Global Ping
- https://computers-are-fast.github.io/
| computer latency | nano seconds | micro seconds | milliseconds | relative |
|---|---|---|---|---|
| L1 cache reference | 0.5 ns | |||
| Branch mispredict | 5.0 ns | |||
| L2 cache reference | 7.0 ns | 14x L1 cache | ||
| Mutex lock/unlock | 25.0 ns | |||
| Main memory reference | 100.0 ns | 20x L2 cache, 200x L1 cache | ||
| Compress 1K bytes with Zippy | 3,000.0 ns | 3 us | ||
| Send 1K bytes over 1 Gbps network | 10,000.0 ns | 10 us | ||
| Read 4K randomly from SSD | 150,000.0 ns | 150 us | ~1GB/sec SSD | |
| Read 1 MB sequentially from memory | 250,000.0 ns | 250 us | ||
| Round trip within same datacenter | 500,000.0 ns | 500 us | 0.5 ms | |
| Read 1 MB sequentially from SSD | 1,000,000.0 ns | 1,000 us | 1 ms | ~1GB/sec SSD, 4X memory |
| Disk seek | 10,000,000.0 ns | 10,000 us | 10 ms | 20x datacenter roundtrip |
| Read 1 MB sequentially from disk | 20,000,000.0 ns | 20,000 us | 20 ms | 80x memory, 20X SSD |
| Send packet CA->Netherlands->CA | 150,000,000.0 ns | 150,000 us | 150 ms |
Misc
| common latency | ms | s |
|---|---|---|
| 120 fps | 8 ms | 1/120 s |
| 60 fps | 16 ms | 1/60 s |
| 24 fps | 41 ms | 1/24 s |
| human lantency | ms | s |
|---|---|---|
| eye blink | 100-150 ms | 0.1-0.5 s |
| human reaction time | 250 ms | 0.25 s |
- Nerve conduction velocity/神经传导速度 ~ 40m/s
- 音速 - 343 m/s
- 光速 - 299,792,458 m / s
Unit
| unit | stand for | n | mean |
|---|---|---|---|
| ns | nano second | 10^9 | 纳秒 |
| us | micro second | 10^6 | 微秒 |
| ms | milli second | 10^3 | 毫秒 |
| s | second | 1 | 秒 |
| ns | us | ms | s |
|---|---|---|---|
| 1 | 10^-3 | 10^-6 | 10^-9 |
| 1000 | 1 | 10^-3 | 10^-6 |
| 10^6 | 1000 | 1 | 10^-3 |
| 10^9 | 10^6 | 1000 | 1 |
datacenter vs region vs zone vs vs cluster vs rack
- datacenter - dc
- 逻辑机房
- 可能在同一个 region
- 相同 dc 内 < 1ms
- 相同 region 内 < 10ms
- 不同 region 则延时不确定 - 可能跨越半个地球
- 低到 < 10ms
- 高到 > 300ms
- cluster
- 逻辑概念
- 通常在一个 dc
- rack
- 不同服务器最近接近的定义
- 相同交换机背板
- region - 区域 - 由多个地区组成
- 独立地理位置
- zone - 地区
- 故障网域