Anwar zianwar

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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

What is a mutex and how does it work

Imagine a big office (your program), with many assets (shared resources) and many employees (threads). For example, all employees share one common resource - a toilet. They have agreed to use a label on a toilet's door (mutex).

When an employee wants to use the toilet he checks a label on a door (locks a mutex). If it is "engaged" he waits (blocks on a mutex), then when it is "free", he enters the toilet and changes the label to

What is a hash and how does it work

Let us start from a practical example. Imagine we are writing a traffic monitoring application. The purpose of application would be to calculate a number of bytes sent by each IP address. To do that, let create a structure that does that accounting:

struct ipstat {

uint32_t ip; /* Source IP address */

Two way iframe communication

The main difference between the two pages is the method of sending messages. Recieving messages is the same in both.

Parent

Send messages to iframe using iframeEl.contentWindow.postMessage Recieve messages using window.addEventListener('message')

iframe

Mac OS X 10.10 Yosemite

Custom recipe to get OS X 10.10 Yosemite running from scratch, setup applications and developer environment. I use this gist to keep track of the important software and steps required to have a functioning system after a semi-annual fresh install. On average, I reinstall each computer from scratch every 6 months, and I do not perform upgrades between distros.

This keeps the system performing at top speeds, clean of trojans, spyware, and ensures that I maintain good organizational practices for my content and backups. I highly recommend this.

You are encouraged to fork this and modify it to your heart's content to match your own needs.

	#!/bin/sh

	###
	# SOME COMMANDS WILL NOT WORK ON macOS (Sierra or newer)
	# For Sierra or newer, see https://github.com/mathiasbynens/dotfiles/blob/master/.macos
	###

	# Alot of these configs have been taken from the various places
	# on the web, most from here
	# https://github.com/mathiasbynens/dotfiles/blob/5b3c8418ed42d93af2e647dc9d122f25cc034871/.osx

	-- AppleScript --

	-- This example is meant as a simple starting point to show how to get the information in the simplest available way.
	-- Keep in mind that when asking for a `return` after another, only the first one will be output.
	-- This method is as good as its JXA counterpart.

	-- Webkit variants include "Safari", "Webkit", "Orion".
	-- Specific editions are valid, including "Safari Technology Preview".
	-- "Safari" Example:
	tell application "Safari" to return name of front document

	if _, err := os.Stat("/path/to/whatever"); os.IsNotExist(err) {
	// path/to/whatever does not exist
	}

	if _, err := os.Stat("/path/to/whatever"); !os.IsNotExist(err) {
	// path/to/whatever exists
	}

	package main

	import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"fmt"
	"io"
	"io/ioutil"
	"os"