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 Send 1K bytes over 1 Gbps network 10,000 ns 0.01 ms Read 4K randomly from SSD* 150,000 ns 0.15 ms Read 1 MB sequentially from memory 250,000 ns 0.25 ms 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 = 10-9 seconds 1 ms = 10-3 seconds * Assuming ~1GB/sec SSD
Wednesday, January 28, 2015
I am not sure if 1% of programmers know it, but it is a great reference, kudos to Jeff Dean and Peter Norvig: Latency Comparison Numbers
Saturday, January 24, 2015
A typical problem that I often have, playing with various repositories and frameworks is how to add already existing project to a remote repository. In this tutorial I show how to do it for a GitHub mostly by using a command line. I assume that git environment is already set up and that there is already a working environment that is able to push/pull data from GitHub. For windows the only thing that one has to do is to install GitHub for windows.
- 1. Create a new repository in GitHub - it means go to GitHub page, login, add a new repository. This is the only step that requires doing something not in a command line. I will create a my-app repository, so it will be available under https://github.com/sagasu/my-app
- 2. Open a git shell.
- 3. Navigate to a project directory. Actually you have to 'cd my-app', and be in a directory with a project files.
- 4. git init
- 5. git add .
- 6. git commit -m 'message'
- 7. git remote add my-app https://github.com/sagasu/my-app
- 8. git push -u my-app master