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

marktheunissen

This playbook has been removed as it is now very outdated.

phgrau

Variables
==========
predefined variables : 
- inventory_hostname (fqdn) (normally the same as ansible.fqdn)
- inventory_hostname_short 

To know the return codes returned by ansible modules, just use plain ansible -vvv to see them : 
ansible -i ~/ansible/arrfab.net/hosts/hosts.cfg -vvv -m copy -a 'src=files/sysinfo dest=/etc/sysinfo' tungstene.arrfab.net
tungstene.arrfab.net | success >> {
    "changed": true, 

miketheman

Adding 2 nodes to an existing 3-node ZooKeeper ensemble without losing the Quorum

Since many deployments may start out with 3 nodes and so little is known about how to grow a cluster from 3 memebrs to 5 members without losing the existing Quorum, here is an example of how this might be achieved.

In this example, all 5 nodes will be running on the same Vagrant host for the purpose of illustration, running on distinct configurations (ports and data directories) without the actual load of clients.

YMMV. Caveat usufructuarius.

Step 1: Have a healthy 3-node ensemble

marcusphi

---
# This has been tested with ansible 1.3 with these commands:
#   ansible-playbook -i hosts ansible_conditionals_examples.yaml --extra-vars="hosts=myhosts isFirstRun=false"
#   ansible-playbook -i hosts ansible_conditionals_examples.yaml --extra-vars="hosts=myhosts isFirstRun=true"
#   ansible-playbook -i hosts ansible_conditionals_examples.yaml --extra-vars="hosts=myhosts"
# NB: The type of the variable is crucial!

- name: Ansible Conditionals Examples
  hosts: $hosts
  vars_files:

mdeeks

init_config:

instances:
    -   host: localhost
        port: 9999
        conf:
            # Young Gen Collectors (Minor Collections)
            - include:
                domain: java.lang
                type: GarbageCollector

chanks

Turning PostgreSQL into a queue serving 10,000 jobs per second

RDBMS-based job queues have been criticized recently for being unable to handle heavy loads. And they deserve it, to some extent, because the queries used to safely lock a job have been pretty hairy. SELECT FOR UPDATE followed by an UPDATE works fine at first, but then you add more workers, and each is trying to SELECT FOR UPDATE the same row (and maybe throwing NOWAIT in there, then catching the errors and retrying), and things slow down.

On top of that, they have to actually update the row to mark it as locked, so the rest of your workers are sitting there waiting while one of them propagates its lock to disk (and the disks of however many servers you're replicating to). QueueClassic got some mileage out of the novel idea of randomly picking a row near the front of the queue to lock, but I can't still seem to get more than an an extra few hundred jobs per second out of it under heavy load.

So, many developers have started going straight t

sebsto

import json, boto

# Connect to IAM with boto
iam = boto.connect_iam(ACCESS_KEY, SECRET_KEY)

# Create user
user_response = iam.create_user('aws-user')

# Create Policy
policy = { 'Version' : '2012-10-17'}

kwk

#!/bin/bash

JQPATH=$(which jq)
if [ "x$JQPATH" == "x" ]; then
  echo "Couldn't find jq executable." 1>&2
  exit 2
fi

set -eu
shopt -s nullglob

prakhar1989

Rich Hickey on becoming a better developer

Rich Hickey • 3 years ago

Sorry, I have to disagree with the entire premise here.

A wide variety of experiences might lead to well-roundedness, but not to greatness, nor even goodness. By constantly switching from one thing to another you are always reaching above your comfort zone, yes, but doing so by resetting your skill and knowledge level to zero.

Mastery comes from a combination of at least several of the following: