https://github.com/medmes/latency

About latency numbers!
https://github.com/medmes/latency

latency performance systems

Last synced: 3 months ago
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About latency numbers!

• Host: GitHub
• URL: https://github.com/medmes/latency
• Owner: medmes
• Created: 2020-05-01T00:08:11.000Z (about 5 years ago)
• Default Branch: master
• Last Pushed: 2020-05-01T15:08:49.000Z (about 5 years ago)
• Last Synced: 2025-02-01T11:16:03.295Z (4 months ago)
• Topics: latency, performance, systems
• Homepage:
• Size: 2.93 KB
• Stars: 1
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# latency numbers

### Latency numbers every programmer should know

    L1 cache reference ......................... 0.5 ns

    Branch mispredict ............................ 5 ns

    L2 cache reference ........................... 7 ns

    Mutex lock/unlock ........................... 25 ns

    Main memory reference ...................... 100 ns             

    Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs

    Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs

    SSD random read ........................ 150,000 ns  = 150 µs

    Read 1 MB sequentially from memory ..... 250,000 ns  = 250 µs

    Round trip within same datacenter ...... 500,000 ns  = 0.5 ms

    Read 1 MB sequentially from SSD* ..... 1,000,000 ns  =   1 ms

    Disk seek ........................... 10,000,000 ns  =  10 ms

    Read 1 MB sequentially from disk .... 20,000,000 ns  =  20 ms

    Send packet CA->Netherlands->CA .... 150,000,000 ns  = 150 ms

Assuming ~1GB/sec SSD

![Visual representation of latencies](http://i.imgur.com/k0t1e.png)

Visual chart provided by [ayshen](https://gist.github.com/ayshen)

Data by [Jeff Dean](http://research.google.com/people/jeff/)

Originally by [Peter Norvig](http://norvig.com/21-days.html#answers)

### Lets multiply all these durations by a billion:

Magnitudes:

### Minute:

    L1 cache reference                  0.5 s         One heart beat (0.5 s)

    Branch mispredict                   5 s           Yawn

    L2 cache reference                  7 s           Long yawn

    Mutex lock/unlock                   25 s          Making a coffee

### Hour:

    Main memory reference               100 s         Brushing your teeth

    Compress 1K bytes with Zippy        50 min        One episode of a TV show (including ad breaks)

### Day:

    Send 2K bytes over 1 Gbps network   5.5 hr        From lunch to end of work day

### Week

    SSD random read                     1.7 days      A normal weekend

    Read 1 MB sequentially from memory  2.9 days      A long weekend

    Round trip within same datacenter   5.8 days      A medium vacation

    Read 1 MB sequentially from SSD    11.6 days      Waiting for almost 2 weeks for a delivery

### Year

    Disk seek                           16.5 weeks    A semester in university

    Read 1 MB sequentially from disk    7.8 months    Almost producing a new human being

    The above 2 together                1 year

### Decade

    Send packet CA->Netherlands->CA     4.8 years     Average time it takes to complete a bachelor's degree