Insanely fast multi-core Node.js script for generating (or regenerating) custom WordPress image sizes (e.g. thumbnails) for very large media libraries

regenerate-thumbnails.js

// Your server must have wp-cli installed (http://wp-cli.org/)

var async = require("async");
var exec = require("child_process").exec;

var cores = 32; // Adjust the number of cores to match your environment
var total = 0;
var finished = 0;

var q = async.queue(function(task, callback) {
	exec(task.command, function(error, stdout, stderr) {
		finished++;
		process.stdout.write("Processing " + total + " images using " + cores + " cores. Progress: " + (100 * (finished / total)).toFixed(2) + "%\r");
		callback();
	});
}, cores);

q.drain = function() {
	console.log("Finished processing " + total + " images using " + cores + " cores.         ");
	process.exit();
};

// Get all media post IDs
exec("wp db query \"SELECT id FROM wp_posts WHERE post_type = 'attachment'\"", {maxBuffer: 1000 * 1024}, function(error, stdout, stderr) {
	var id = stdout.split(/\n/);
	for (var i = 1; i < id.length; i++) {
		q.push({command: "wp media regenerate " + id[i]});
		total++;
	}
});

Awesome! This still works. Install the npm modules first (npm install async, npm install child_process). This is a rocket. Then run node regenerate-thumbnails.js in the root. Thank you.