No Callbacks, No Threads - RailsConf 2010

No Callbacks, No Threads & Ruby 1.9 @igrigorikhttp://bit.ly/ruby-stack

No Callbacks, No Threads & Ruby 1.9

Ilya Grigorik@igrigorik

async & co-operative web-servers

The slides… Twitter My blog

The state of art is not good enough.(we’ve been stuck in the same local minima for several years)

require "active_record” ActiveRecord::Base.establish_connection( :adapter => "mysql", :username => "root", :database => "database", :pool => 5) threads = []10.times do |n| threads << Thread.new { ActiveRecord::Base.connection_pool.with_connection do |conn| res = conn.execute("select sleep(1)") end }end threads.each { |t| t.join }

The “Experiment”vanilla everything…

require "active_record” ActiveRecord::Base.establish_connection( :adapter => "mysql", :username => "root", :database => "database", :pool => 5) threads = []10.times do |n| threads << Thread.new { ActiveRecord::Base.connection_pool.with_connection do |conn| res = conn.execute("select sleep(1)") end }end threads.each { |t| t.join }

# time ruby activerecord-pool.rb## real 0m10.663s# user 0m0.405s# sys 0m0.201s

5 shared connections

% power loss

> 50% power loss!?

Drivers

Ruby VM

Network

MySQLMongo

PSQL Couch…

MongrelPassenger

Unicorn

Threads

Fibers GIL …

Drivers

Ruby VM

Network

MySQLMongo

PSQL Couch…

MongrelPassenger

Unicorn

Threads

Fibers GIL …

We’re as fast as the slowest component

Concurrency is a myth in Ruby(with a few caveats, of course)

Global Interpreter Lock is a mutual exclusion lock held by a programming language interpreter thread to avoid sharing code that is not thread-safe with other threads.

There is always one GIL for one interpreter process.

http://bit.ly/ruby-gil

Concurrency is a myth in Rubystill no concurrency in Ruby 1.9

N-M thread pool in Ruby 1.9…Better but still the same problem!

Concurrency is a myth in Rubystill no concurrency in Ruby 1.9

Nick – tomorrow @ 11:45am

Avoid locking interpreter threads at all costslet’s say you’re writing an extension…

Blocks entireRuby VM

Not as bad, butavoid it still..

Will fetch_xyz() block the VM?when was the last time you asked yourself this question?

mysql.gem under the hood

require 'rubygems’require 'sequel'

DB = Sequel.connect('mysql://root@localhost/test')

while true DB['select sleep(1)'].select.firstend

22:10:00.218438 mysql_real_query(0x02740000, "select sleep(1)", 15) = 0 <1.001100>22:10:01.241679 mysql_real_query(0x02740000, "select sleep(1)", 15) = 0 <1.000812>

ltrace –ttTg -x mysql_real_query –p ./example.rb

Blocking 1s call!

http://bit.ly/c3Pt3f

gem install mysqlwhat you didn’t know…

1. Blocking calls to mysql_real_query2. mysql_real_query requires an OS thread3. Blocking on mysql_real_query blocks the Ruby VM4. Aka, “select sleep(1)” blocks the entire Ruby runtime for 1s

(ouch)

mysqlplus.gem under the hood

static VALUE async_query(int argc, VALUE* argv, VALUE obj) { ... send_query( obj, sql ); ... schedule_query( obj, timeout); ... return get_result(obj); }

static void schedule_query(VALUE obj, VALUE timeout) { ... struct timeval tv = { tv_sec: timeout, tv_usec: 0 };

for(;;){ FD_ZERO(&read); FD_SET(m->net.fd, &read);

ret = rb_thread_select(m->net.fd + 1, &read, NULL, NULL, &tv); ... if (m->status == MYSQL_STATUS_READY) break; }}

send query and block

Ruby: select() = C: rb_thread_select()

mysqlplus.gem + ruby select

spinning in select

Step 1: Fix the driversMany of our DB drivers don’t respect the underlying Ruby VM. Don’t blame the VM.

WEBRick

Drivers

Ruby VM

Network

Mongrel made Rails viablestill powers a lot of Rails apps today

Rails rediscovers Apachethe worker/forker model…

An exclusive Ruby VM for EACH requestam I the only one who thinks this is terrible?

*nix IPC is fast! Woo!

Full Ruby VM

An exclusive Ruby VM for EACH requestam I the only one who thinks this is terrible?

Robustness? That sounds like a bug.

“Does not care if your application is thread-safe or not, workers all run within their own isolated address space and only serve one client at a time for maximum robustness.”

Step 2: consider entire stackThe driver, the web-server, and the networkmust all work together.

1. Node imposes the full-stack requirements2. Node imposes async drivers3. Node imposes async frameworks

Surprise: Node is “fast”

We can ignore the performanceissues at our own peril

or, we can just fix the problem

I’ll take Ruby over JSgem install eventmachine

EventMachine Reactorconcurrency without thread

EventMachine: The Speed DemonWednesday @ 11:45am – Aman Gupta

while true do timers

network_ioother_io

p "Starting"

EM.run do p "Running in EM reactor"end

p ”won’t get here"

Non-blocking IO requires non-blocking drivers:

AMQP http://github.com/tmm1/amqpMySQLPlus http://github.com/igrigorik/em-mysqlplus Memcached http://github.com/astro/remcached DNS http://github.com/astro/em-dns Redis http://github.com/madsimian/em-redis MongoDB http://github.com/tmm1/rmongo HTTPRequest http://github.com/igrigorik/em-http-request WebSocket http://github.com/igrigorik/em-websocket Amazon S3 http://github.com/peritor/happening

And many others: http://wiki.github.com/eventmachine/eventmachine/protocol-implementations

em-mysqlplus: exampleasync MySQL driver

EventMachine.run do conn = EventMachine::MySQL.new(:host => 'localhost') query = conn.query("select sleep(1)") query.callback { |res| p res.all_hashes } query.errback { |res| p res.all_hashes }

puts ”executing…”end

# > ruby em-mysql-test.rb## executing…# [{"sleep(1)"=>"0"}]

gem install em-mysqlplus

callback fired 1s after “executing”

em-mysqlplus: under the hoodmysqlplus + reactor loop

non-blocking driverrequire 'mysqlplus'

def connect(opts) conn = connect_socket(opts) EM.watch(conn.socket, EventMachine::MySQLConnection, conn, opts, self)end

def connect_socket(opts) conn = Mysql.init

conn.real_connect(host, user, pass, db, port, socket, ...) conn.reconnect = false connend

EM.watch: reactor will poll & notify

em-mysqlplusmysqlplus + reactor loop

Features:

- Maintains C-based mysql gem API- Deferrables for every query with callback & errback- Connection query queue - pile 'em up! - Auto-reconnect on disconnects- Auto-retry on deadlocks

http://github.com/igrigorik/em-mysqlplus

and this callback goes to…

We can do better than node.jsall the benefits of evented code without the drawbacks

Ruby 1.9 Fibersand cooperative scheduling

Ruby 1.9 Fibers are a means of creating code blocks which can be paused and resumed by our application (think lightweight threads, minus the thread scheduler and less overhead).

f = Fiber.new { while true do Fiber.yield "Hi” end}

p f.resume # => Hip f.resume # => Hip f.resume # => Hi

Manual / cooperative scheduling!

http://bit.ly/d2hYw0

Ruby 1.9 Fibersand cooperative scheduling

http://bit.ly/aesXy5

Fibers vs Threads: creation time much lower

Fibers vs Threads: memory usage is much lower

Untangling Evented Code with Fibershttp://bit.ly/d2hYw0

def query(sql) f = Fiber.current conn = EventMachine::MySQL.new(:host => 'localhost') q = conn.query(sql) c.callback { f.resume(conn) } c.errback { f.resume(conn) } return Fiber.yieldend EventMachine.run do Fiber.new { res = query('select sleep(1)') puts "Results: #{res.fetch_row.first}" }.resumeend

Exception, async!

1. Wrap into a continuation

2. Pause the continuation

3. Resume the continuation

em-synchrony: simple evented programmingbest of both worlds…

Good news, you don’t even have to muck around with Fibers!

gem install em-synchrony

- Fiber aware connection pool with sync/async query support- Multi request interface which accepts any callback enabled client - Fibered iterator to allow concurrency control & mixing of sync / async- em-http-request: .get, etc are synchronous, while .aget, etc are async- em-mysqlplus: .query is synchronous, while .aquery is async- remcached: .get, etc, and .multi_* methods are synchronous

http://github.com/igrigorik/em-synchrony

Async under the hood

require "em-synchrony/em-mysqlplus"

EventMachine.synchrony do db = EventMachine::MySQL.new(host: "localhost")

res = db.query("select sleep(1)") puts res

EventMachine.stopend

require "em-synchrony/em-mysqlplus"

EventMachine.synchrony do db = EventMachine::MySQL.new(host: "localhost")

res = db.query("select sleep(1)") puts res

EventMachine.stopend

Drivers

Ruby VM

Network

Fibers

EM-HTTP, EM-MySQL, EM-Jack, etc.

Async-rack

One VM, full concurrency, network-boundRuby 1.9, Fibers, Thin: in production!

Goliath

Async Railswith EventMachine & MySQL

development: adapter: em_mysqlplus database: widgets pool: 5 timeout: 5000

git clone git://github.com/igrigorik/em-mysqlplus.gitgit checkout activerecordrake install

database.yml

require 'em-activerecord’require 'rack/fiber_pool'

# Run each request in a Fiberconfig.middleware.use Rack::FiberPoolconfig.threadsafe!

environment.rb

Async Railswith EventMachine & MySQL

class WidgetsController < ApplicationController def index Widget.find_by_sql("select sleep(1)") render :text => "Oh hai” endend

ab –c 5 –n 10 http://127.0.0.1:3000/widgets

Server Software: thinServer Hostname: 127.0.0.1Server Port: 3000

Document Path: /widgets/Document Length: 6 bytes

Concurrency Level: 5Time taken for tests: 2.210 secondsComplete requests: 10Failed requests: 0Requests per second: 4.53 [#/sec] (mean)

woot! Fiber DB pool at work.

Not only is it doable… it already works.

git clone git://…./igrigorik/mysqlplusgit checkout activerecordrake install

Ruby 1.9 + Rails 3 + new stack

Order of magnitude better performance

(aka, enough of a reason to actually switch)

What do you think?

The state of art is not good enough, in fact, it’s terrible!

Let’s fix it.

Untangling Evented Code with Ruby Fibers:http://www.igvita.com/2010/03/22/untangling-evented-code-with-ruby-fibers/

Fibers & Cooperative Scheduling in Ruby:http://www.igvita.com/2009/05/13/fibers-cooperative-scheduling-in-ruby/

EM-Synchrony:http://github.com/igrigorik/em-synchrony

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