latency.txt

Latency Comparison Numbers
--------------------------
L1 cache reference                            0.5 ns
访问一级缓存
Branch mispredict                             5   ns
分支误预测
L2 cache reference                            7   ns             14x L1 cache
访问二级缓存
Mutex lock/unlock                            25   ns
互斥锁 加锁/解锁
Main memory reference                       100   ns             20x L2 cache, 200x L1 cache
访问主存
Compress 1K bytes with Zippy              3,000   ns
用 zippy 压缩 1k 的内容
Send 1K bytes over 1 Gbps network        10,000   ns    0.01 ms
1Gb 的网络上发送 1k 的内容
Read 4K randomly from SSD*              150,000   ns    0.15 ms
从固体硬盘上读取 4k 的内容
Read 1 MB sequentially from memory      250,000   ns    0.25 ms
从内存中顺序读取 1M 的内容
Round trip within same datacenter       500,000   ns    0.5  ms
Read 1 MB sequentially from SSD*      1,000,000   ns    1    ms  4X memory
Disk seek                            10,000,000   ns   10    ms  20x datacenter roundtrip
Read 1 MB sequentially from disk     20,000,000   ns   20    ms  80x memory, 20X SSD
Send packet CA->Netherlands->CA     150,000,000   ns  150    ms

Notes
-----
1 ns = 10E-9 seconds
1 ms = 10E-3 seconds
* Assuming ~1GB/sec SSD

Credit
------
By Jeff Dean:               http://research.google.com/people/jeff/
Originally by Peter Norvig: http://norvig.com/21-days.html#answers

Contributions
-------------
Some updates from:                      https://gist.github.com/2843375
Great 'humanized' comparison version:   https://gist.github.com/2843375
Visual comparison chart:                http://i.imgur.com/k0t1e.png
Nice animated presentation of the data: http://prezi.com/pdkvgys-r0y6/latency-numbers-for-programmers-web-development/