[置顶] Every Programmer Should Know These Latency Numbers
转自: https://dzone.com/articles/every-programmer-should-know
Every Programmer Should Know These Latency Numbers
Relic. Quickly learn how to use Docker
and containers in general to create packaged images for easy management, testing, and deployment of software.
This is interesting stuff; Jonas Bonér organized some general some latency data by
Peter Norvig as a Gist, and others expanded on it. What's interesting is how, scaling time up by a billion, converts a CPU instruction cycle into approximately one heartbeat, and yields a
disk seek time of "a semester in university".
### 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 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
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