Jeff Dean Numbers

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"Jeff Dean numbers" refers to The Latency Numbers Every Programmer Should Know, a famous reference list of computer hardware operation timings compiled by legendary Google engineer Jeff Dean. Engineers use these metrics for quick back-of-the-envelope estimations to see how system designs will perform.

Operation	ns	µs	ms	note
L1 cache reference	0.5 ns
Branch mispredict	5 ns
L2 cache reference	7 ns			14x L1 cache
Mutex lock/unlock	25 ns
Main memory reference	100 ns			20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy	3,000 ns	3 µs
Send 1K bytes over 1 Gbps network	10,000 ns	10 µs
Read 4K randomly from SSD*	150,000 ns	150 µs		~1GB/sec SSD
Read 1 MB sequentially from memory	250,000 ns	250 µs
Round trip within same datacenter	500,000 ns	500 µs
Read 1 MB sequentially from SSD*	1,000,000 ns	1,000 µs	1 ms	~1GB/sec SSD, 4X memory
Disk seek	10,000,000 ns	10,000 µs	10 ms	20x datacenter roundtrip
Read 1 MB sequentially from disk	20,000,000 ns	20,000 µs	20 ms	80x memory, 20X SSD
Send packet CA -> Netherlands -> CA	150,000,000 ns	150,000 µs	150 ms

Notes

1 ns = 10^-9 seconds 1 us = 10^-6 seconds = 1,000 ns 1 ms = 10^-3 seconds = 1,000 us = 1,000,000 ns

Credit

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

Contributions

'Humanized' comparison: https://gist.github.com/hellerbarde/2843375 Visual comparison chart: http://i.imgur.com/k0t1e.png Interactive Prezi version: https://prezi.com/pdkvgys-r0y6/latency-numbers-for-programmers-web-development/latency.txt