From 4646b0942c421b91f40c6bfead9de4703cedabc6 Mon Sep 17 00:00:00 2001 From: Donne Martin Date: Thu, 2 Mar 2017 19:48:45 -0800 Subject: [PATCH] Add Latency numbers every programmer should know section --- README.md | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) diff --git a/README.md b/README.md index db9580f..98b1fd7 100644 --- a/README.md +++ b/README.md @@ -1667,3 +1667,51 @@ Power Exact Value Approx Value Bytes #### Source(s) and further reading * [Powers of two](https://en.wikipedia.org/wiki/Power_of_two) + +### 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 + +#### Latency numbers visualized + +![](https://camo.githubusercontent.com/77f72259e1eb58596b564d1ad823af1853bc60a3/687474703a2f2f692e696d6775722e636f6d2f6b307431652e706e67) + +#### 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)