46 lines
2.7 KiB
Markdown
46 lines
2.7 KiB
Markdown
### Latency numbers every programmer should know
|
|
---
|
|
Latency Comparison Numbers
|
|
--------------------------
|
|
L1 cache reference 0.5 ns
|
|
Branch mispredict 5 ns
|
|
L2 cache reference 7 ns 14x L1 cache
|
|
Mutex lock/unlock 100 ns
|
|
Main memory reference 100 ns 20x L2 cache, 200x L1 cache
|
|
Compress 1K bytes with Zippy 10,000 ns 10 us
|
|
Send 1 KB bytes over 1 Gbps network 10,000 ns 10 us
|
|
Read 4 KB randomly from SSD- 150,000 ns 150 us ~1GB/sec SSD
|
|
Read 1 MB sequentially from memory 250,000 ns 250 us
|
|
Round trip within same datacenter 500,000 ns 500 us
|
|
Read 1 MB sequentially from SSD- 1,000,000 ns 1,000 us 1 ms ~1GB/sec SSD, 4X memory
|
|
Disk seek 10,000,000 ns 10,000 us 10 ms 20x datacenter roundtrip
|
|
Read 1 MB sequentially from 1 Gbps 10,000,000 ns 10,000 us 10 ms 40x memory, 10X SSD
|
|
Read 1 MB sequentially from disk 30,000,000 ns 30,000 us 30 ms 120x memory, 30X SSD
|
|
Send packet CA->Netherlands->CA 150,000,000 ns 150,000 us 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
|
|
|
|
|
|
Handy metrics based on numbers above:
|
|
|
|
- Read sequentially from disk at 30 MB/s
|
|
- Read sequentially from 1 Gbps Ethernet at 100 MB/s
|
|
- Read sequentially from SSD at 1 GB/s
|
|
- Read sequentially from main memory at 4 GB/s
|
|
- 6-7 world-wide round trips per second
|
|
- 2,000 round trips per second within a data center
|
|
|
|
#### [](https://github.com/donnemartin/system-design-primer#latency-numbers-visualized) Latency numbers visualized
|
|
|
|
[ ](https://camo.githubusercontent.com/77f72259e1eb58596b564d1ad823af1853bc60a3/687474703a2f2f692e696d6775722e636f6d2f6b307431652e706e67)
|
|
|
|
#### [](https://github.com/donnemartin/system-design-primer#sources-and-further-reading-14) Source(s) and further reading
|
|
|
|
- [Latency numbers every programmer should know - 1](https://gist.github.com/jboner/2841832)
|
|
- [Latency numbers every programmer should know - 2](https://gist.github.com/hellerbarde/2843375)
|
|
- [Designs, lessons, and advice from building large distributed systems](http://www.cs.cornell.edu/projects/ladis2009/talks/dean-keynote-ladis2009.pdf)
|
|
- [Software Engineering Advice from Building Large-Scale Distributed Systems](https://static.googleusercontent.com/media/research.google.com/en//people/jeff/stanford-295-talk.pdf) |