hellerbarde

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

crtr0

// set-up a connection between the client and the server
var socket = io.connect();

// let's assume that the client page, once rendered, knows what room it wants to join
var room = "abc123";

socket.on('connect', function() {
   // Connected, let's sign-up for to receive messages for this room
   socket.emit('room', room);
});

stephenhardy

-- Remove the history from 
rm -rf .git

-- recreate the repos from the current content only
git init
git add .
git commit -m "Initial commit"

-- push to the github remote repos ensuring you overwrite history
git remote add origin git@github.com:<YOUR ACCOUNT>/<YOUR REPOS>.git

hubgit

Anonymising PDFs

PDF metadata

Metadata in PDF files can be stored in at least two places:

• the Info Dictionary, a limited set of key/value pairs
• XMP packets, which contain RDF statements expressed as XML

PDF files

DecisionNerd

#!/bin/bash
# CSV to JSON converter using BASH
# original script from http://blog.secaserver.com/2013/12/convert-csv-json-bash/
# thanks SecaGuy!
# Usage ./csv2json.sh input.csv > output.json
 
input=$1
 
[ -z $1 ] && echo "No CSV input file specified" && exit 1
[ ! -e $input ] && echo "Unable to locate $1" && exit 1

bastman

Docker - How to cleanup (unused) resources

Once in a while, you may need to cleanup resources (containers, volumes, images, networks) ...

delete volumes

// see: https://github.com/chadoe/docker-cleanup-volumes

$ docker volume rm $(docker volume ls -qf dangling=true)

$ docker volume ls -qf dangling=true | xargs -r docker volume rm

olih

Processing JSON using jq

jq is useful to slice, filter, map and transform structured json data.

Installing jq

On Mac OS

brew install jq

protrolium

Install ImageMagick

brew install ImageMagick

Pull specific region of frames from video file w/ ffmpeg

ffmpeg -ss 14:55 -i video.mkv -t 5 -s 480x270 -f image2 %04d.png

• -ss 14:55 gives the timestamp where I want FFmpeg to start, as a duration string.
  
• -t 5 says how much I want FFmpeg to decode, using the same duration syntax as for -ss.
  
• -s 480x270 tells FFmpeg to resize the video output to 480 by 270 pixels.
  
• -f image2 selects the output format, a series of still images — make sure there are leading zeros in filename.
  

leonardofed

A curated list of AWS resources to prepare for the AWS Certifications

A curated list of awesome AWS resources you need to prepare for the all 5 AWS Certifications. This gist will include: open source repos, blogs & blogposts, ebooks, PDF, whitepapers, video courses, free lecture, slides, sample test and many other resources.

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sebastianwebber

Uber facts

Original posts/information

Migrating Uber from MySQL to PostgreSQL

Key points

• ~50GB MySQL Application
• Main motivation: PostGis
• Migration made with a custom tool(xml2pgcopy) and mysqldump on 45min