Latency Numbers Every Programmer Should Know

Latency Comparison Numbers


Operation Time in ns Time in ms Comment
L1 cache reference 0.5
Branch mispredict 5
L2 cache reference 7 14x L1 cache
Mutex lock/unlock 25
Main memory reference 100 20x L2 cache, 200x
Compress 1K bytes with Zip 3,000
Send 1K bytes over 1 Gbps network 10,000 0.01
Read 4K randomly from SSD 150,000 0.15
Read 1 MB sequentially from memory 250,000 0.25
Round trip within same datacenter 500,000 0.5
Read 1 MB sequentially from SSD 1,000,000 1 4X memory
Disk seek 10,000,000 10 20x datacenter roundtrip
Read 1 MB sequentially from disk 20,000,000 20 80x memory, 20X SSD
Send packet CA->Netherlands->CA 150,000,000 150

Install Hadoop stack on OSX

SSH Setup and Key Generation

SSH setup is required to do different operations on a cluster such as starting, stopping, distributed daemon shell operations. To authenticate different users of Hadoop, it is required to provide public/private key pair for a Hadoop user and share it with different users.

Hello World!

1 class HelloWorldApp {
2     public static void main(String[] args) {
3         System.out.println("Hello World!"); // Display the string.
4     }
5 }