Off The Rails

Oﬀ The Rails Sam Saﬀron

About me •  Discourse co-‐founder •  Full 4me open
source developer •  Remote worker •  Gem author •  Performance enthusiast •  Stack Overflow employee #8 •  samsaffron.com •  @samsaffron

Omakase v2 Free Performance fast_xor fast_xs
fast_blank hiredis Caching message_bus Anonymous cache NGINX Profiling and Diagnos4cs rack_mini_profiler flamegraph rbtrace Development logster pry beOer_errors + binding_of_caller rack-‐mini-‐profiler fast assets rake autospec Live reload CSS Messaging message_bus Logging logster Serializa4on ac4ve_model_serializers oj

Omakase Demo

gem install message_bus

MessageBus.subscribe("/chat") do |msg| pp msg
end MessageBus.publish "/chat", ["hello","there"] # global_id=1 # message_id=1 # channel="/chat" # data=["hello", "there"]

MessageBus.user_id_lookup do |env| lookup_user_id(env) end
MessageBus.publish "/users/1", ["hello","there"], user_id: 1 // <script src="message-‐bus.js" type="text/javascript"></script> MessageBus.subscribe("/users/1", function(msg){ console.log(msg); }); Ruby JavaScript

message_bus features • Long polling / polling • Security (group /
user) • Reliable playback (catch up) • Eﬃcient transport (mul4plexer) • Mul4site support

Rack Hijack works on unicorn/puma/ passenger run lambda{|env|
io = env['rack.hijack'].call Thread.new do sleep 1 io.write "HTTP/1.1 200\r\n" io.write "Connection: close\r\n" io.write "Content-‐Length: 2\r\n" io.write "\r\n" io.write "OK" io.close end [418,{},"NOT DEFINED IN SPEC"] } % ab -‐c 100 -‐n 100 hOp://localhost:8080/ … Percentage of the requests served within a certain 4me 50% 1076 100% 1084 (longest request) 100 concurrent requests All sleep for 1 second Served with 1.08 seconds Unicorn/Puma or Passenger

message_bus, ready for producEon • Uses rack.hijack (and thin.async for thin)
• In produc4on in Discourse for 2+ years • Minimal dependencies (redis and rack only) • can be ported to pg or memory • Runs inside your Rails app as middleware, no need for extra ports / apps

What about AcEon Cable? •  No code available to review,
but … many open ques4ons •  Websockets only ?! •  Reliable message ordering ?! Ability to catch up ?! •  Event Machine?! Celluloid?!

What about web sockets?

What about web sockets? •  Ini4al version supported it
•  Reliable pub/sub s4ll required •  Fallback logic s4ll required (6 connec4on per browser, less on phones) •  HTTPS required •  HAProxy hacks may be required •  Hard to debug •  Not signiﬁcantly beOer than long polling •  PR welcome

QuesEons?

hJp://chat.samsaﬀron.com

gem install lru_redux

cache = LruRedux::Cache.new(2) cache[:a] = "1" cache[:b] =
"2" cache[:c] = "3" p cache.to_a [[:c, "3"], [:b, "2"]]

lru_redux • LruRedux::TTL::Cache – Cache with 4me-‐to-‐live • Thread safe versions:
LruRedux::ThreadSafeCache etc. • Fastest exis4ng TTL and LRU cache for Ruby • Ruby 1.9 and up due to ordered seman4cs in Hash

Now let’s splash in some message_bus

# on server 1 @cache = DistributedCache.new("site_customization")
# on server 2 @cache = DistributedCache.new("site_customization") @cache["foo"] = "bar" # on server 1 puts @cache["foo"] # "bar"

Performance is a feature • Discourse op4mizes for adop4on • Needs
to be fast on a $10 a month vps • Constant proﬁling and tuning is also a feature

gem install memory_proﬁler

memory_proﬁler crash course require 'memory_profiler' ENV['RAILS_ENV']="production" MemoryProfiler.report
do require '/Users/sam/Source/discourse/config/environment' I18n.t(:posts) Rails.application.routes.recognize_path('abc') rescue nil User.first end.pretty_print Measure memory usage for boot

AllocaEon reports • Directly relates to overall performance • May have
minimal impact on overall process memory

Discourse boot (allocated) allocated memory by gem -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐
110297190 activesupport-‐4.1.10 30253712 actionpack-‐4.1.10 30242485 rubygems 17451588 2.2.2/lib 16160100 activerecord-‐4.1.10 11930648 mime-‐types-‐1.25.1 9958591 bundler-‐1.10.2 6640523 pg-‐0.18.1 allocated memory by file -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ 89200261 active_support/dependencies.rb 12401276 rubygems/specification.rb 11930648 mime-‐types-‐1.25.1/lib/mime/types.rb 9905902 kernel_require.rb 6544073 pg-‐0.18.1/lib/pg/basic_type_mapping.rb 5681212 action_dispatch/routing/mapper.rb 4665127 journey/gtg/builder.rb 4417058 action_dispatch/routing/route_set.rb 3309612 rubygems/stub_specification.rb 3301511 active_support/core_ext/class/attribute.rb

Discourse boot strings (allocated) 40833 "\n"
22950 ac4ve_support/dependencies.rb:247 3418 rubygems/core_ext/kernel_require.rb:54 … 16423 "" 3421 ac4on_dispatch/journey/nodes/node.rb:33 1643 mime/types.rb:303 1643 mime-‐types-‐1.25.1/lib/mime/types.rb:304 …. 13896 "rake" 13588 bundler/spec_set.rb:111 …. 10731 "applica4on" 3558 mime-‐types-‐1.25.1/lib/mime/types.rb:303 1186 mime-‐types-‐1.25.1/lib/mime/types.rb:427 1186 mime-‐types-‐1.25.1/lib/mime/types.rb:304 1186 mime-‐types-‐1.25.1/lib/mime/types.rb:426 3157 "ruby" 1476 bundler/spec_set.rb:134 1151 rubygems/speciﬁca4on.rb:1850 276 rubygems/stub_speciﬁca4on.rb:21 184 bundler-‐1.10.2/lib/bundler/index.rb:71 The String “\n” is allocated 40833 4mes on boot!

RetenEon reports • How many objects are leu auer block executes?
• Directly relates to GC performance • Directly relates to memory usage

Discourse boot (retained) retained memory by gem -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐
32882335 activesupport-‐4.1.10 6337743 actionpack-‐4.1.10 5744771 activerecord-‐4.1.10 5223057 rubygems 3797283 2.2.2/lib 2431896 mime-‐types-‐1.25.1 2428612 bundler-‐1.10.2 2225017 message_bus-‐1.0.12 2175834 discourse/lib Careful threads are expensive retained memory by location -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ 27361858 active_support/dependencies.rb:247 3778810 rubygems/core_ext/kernel_require.rb:54 1050232 lib/discourse.rb:335 1050232 message_bus-‐1.0.12/lib/message_bus.rb:374 1050232 message_bus-‐1.0.12/lib/message_bus/ timer_thread.rb:21 715906 bundler-‐1.10.2/lib/bundler/runtime.rb:76 641448 active_support/core_ext/class/attribute.rb:8 607917 active_support/core_ext/module/delegation.rb 434136 mime-‐types-‐1.25.1/lib/mime/types.rb:820

Discourse boot (retained) retained objects by gem -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐
69380 activesupport-‐4.1.10 37701 actionpack-‐4.1.10 25410 mime-‐types-‐1.25.1 21817 rubygems 13889 activerecord-‐4.1.10 13489 2.2.2/lib 9111 bundler-‐1.10.2 6441 2.2.0 5396 discourse/lib 4763 tzinfo-‐1.2.2 4044 active_model_serializers-‐0.8.3 3487 railties-‐4.1.10 3079 pg-‐0.18.1 retained objects by class -‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐-‐ 124694 String 33655 RubyVM::InstructionSequence 26591 Array 9565 Hash 9279 Proc 9202 RubyVM::Env 3739 ActionDispatch::Journey::Nodes::Cat 3575 Class 3291 Regexp 3188 Symbol 1643 MIME::Type 1592 Gem::Requirement 1589 ActionDispatch::Journey::Nodes::Slash 1265 Module 1195 ActionDispatch::Journey::Nodes::Literal 1044 Gem::Dependency

Using memory proﬁler to opEmise pluck # CREATE TABLE products(id
int, in_stock boolean, price int, tax int) # ActiveRecord version 4.2.1 ActiveRecord::Base.establish_connection({ adapter: 'postgresql', database: 'test' }) MemoryProfiler.report do Product.limit(10).pluck(:price, :tax) end.pretty_print 286 objects allocated 25K byte allocated

InteresEng data points • The string “Product” allocated 28 4mes
• Numbers are allocated as string • String “price” allocated 3 4mes • Ac4veRecord::Result allocates 4K

What if we had no AcEveRecord? MemoryProfiler.report do
raw_connection.exec("SELECT price, tax FROM products LIMIT 10").values .map{|row| row.map{|col| col.to_i}} end.pretty_print 44 objects allocated (was 286) 3.7K bytes allocated (was 25K) 21 Strings allocated, but we are only selec4ng numbers, WHY?

PG type mapping, new in pg 0.18 type_map = PG::BasicTypeMapForResults.new(raw_connection)
MemoryProfiler.report do result = raw_connection.exec("SELECT price, tax FROM products LIMIT 10") result.type_map = type_map result.values end.pretty_print 13 objects allocated (was 286) 1.1K bytes allocated (was 25K) Shout out to Lars Kanis for building this

BackporEng Fast Pluck into Rails 4 • 87 lines of code
at: discourse/lib/freedom_patches/ fast_pluck.rb • 100% backwards compat (works on Rails 4.1 / 4.2) • Uses new PG type map • Reduce alloca4ons from 286 to 198 • Reduce memory allocated from 25K to 18K • Will not be backported into Rails 4.2

Fast pluck vs pluck 19200 16900 7850
1350 17649 12584 3468 440 10 100 1000 10000 Pluck vs Fast Pluck (higher is be?er) Fast Pluck (ops/sec) Pluck 2 4mes faster 1000 rows

The compelling sell of AcEveRecord cars = Car.all cars
= cars.where(color: color) if color cars = cars.where('max_speed > ?', max_speed) if max_speed cars = cars.select('make, max_speed') cars.each do |car| puts "make: #{car.make} max_speed: #{car.max_speed}" end

AcEveRecord Simple Elegant Flexible Ineﬃcient Not
SQL

Can we do the same by hand? sql = "select
* from cars " and_or_where = "where" if color sql << "where color = '#{PG::Connection.escape(color)}'" and_or_where = "and" end sql << "#{and_or_where} max_speed = '#{max_speed}'" if max_speed connection.exec(sql).each |row| puts "make: #{row["make"]} max_speed: #{row["max_speed"]}" end

Doing it Wrong™ Incomprehensible FAST Risky Yes
SQL

SqlBuilder a sane alternaEve builder = SqlBuilder.new("select * from cars
/*where*/") builder.where("color = :color", color: color) if color builder.where("max_speed = :max_speed", max_speed: max_speed) if max_speed builder.map_exec(Car).each do |row| puts "make: #{row.make} max_speed: #{row.max_speed}" end

SqlBuilder Yes SQL Fast Sane Tiny –
approx 120 lines of code discourse/lib/sql_builder.rb

How fast is this? 0 5 10
15 20 25 30 1 Row 100 Rows 1000 Rows Raw SqlBuilder Ac4ve Record hOps://gist.github.com/SamSaﬀron/9077b632475a4fe0d57b K opera4on/sec (2 columns per row)

A story about Stack Overﬂow

“As soon I started measuring I no4ced that even
though the SQL for this takes 12 milliseconds, the total 4me it takes to execute the above code is much higher, proﬁling shows a 90 ms execuHon Hme.” … so we created Dapper …

What is Dapper? public class Dog {
public int? Age { get; set; } public Guid Id { get; set; } public string Name { get; set; } public ﬂoat? Weight { get; set; } public int IgnoredProperty { get { return 1; } } } var guid = Guid.NewGuid(); var dog = connec4on.Query<Dog>( "select Age = @Age, Id = @Id", new { Age = (int?)null, Id = guid });

AcEve Record needs Dapper • A simple “ultra eﬃcient” standalone SQL
-‐> object mapper • Small code base • Standalone gem • Handle parameters • Interoperable with Rails • All queries run through object mapper • Provide a “blessed” eﬃcient SQL story

How this could look? # Ac4veSQL sql = "select
* from cars limit :limit" cars = Mapper.new(car) .query(sql, limit: 10) # Ac4veRecord cars[0].make = "Ferrari" cars[0].save!

Job scheduling • Background jobs: Sidekiq (without ﬁbers due to
v8) • Regular jobs: Discourse Scheduler • Lightweight jobs: Discourse Defer, runs between requests

Lightweight jobs ObjectSpace.each_object(Unicorn::HttpServer) do |s| s.extend(Scheduler::Defer::Unicorn)
end module Unicorn def process_client(client) Defer.pause super(client) Defer.do_all_work Defer.resume end end

Lightweight jobs Scheduler::Defer.later "track view" do track_page_view(topic,
user) end

Source maps in producEon •  Using uglifyjs directly is signiﬁcantly
faster, 6x faster on some ﬁles •  GSOC project to improve this •  uglifyjs command line makes it simple to add source maps •  Discourse -‐> lib/tasks/assets.rake def compress_node(from,to) to_path = "#{assets_path}/#{to}” source_map_root = (d=File.dirname(from)) == "." ? "/assets" : "/assets/#{d}” cmd = "uglifyjs '#{assets_path}/#{from}' -‐p relaHve -‐c -‐m -‐o '#{to_path}' -‐-‐source-‐map-‐root '#{source_map_root}' -‐-‐source-‐map '#{assets_path}/#{to}.map' -‐-‐source-‐map-‐url '/assets/#{to}.map’” STDERR.puts cmd `#{cmd} 2>&1` end

Anonymous Cache • Dras4cally improves performance • Before: 52 ms per
request to home page • Auer: 1.6 ms per request to home page • Redis backend (redis.setex) • lib/middleware/anonymous_cache.rb

Anonymous Cache • Vast majority of traﬃc is anonymous • Caching
logic is tricky: •  Is it mobile? •  Is it a web crawler? •  Is user logged on? • Implemented as Rack middleware, early in chain

OpEmizing for Development • rake autospec • beOer_errors • rack-‐mini-‐proﬁler
• logster • Fast browser reload 4mes • Live CSS refresh thanks to message_bus

rake autospec • Like guard but… • Interrupt exis4ng test runs
• Focus on failure • Demo

Faster browser reloads in Development 915 ﬁles

Yay, it loads fast! L One big giant
hard to debug ﬁle

eval("var hello=1;\ndebugger;\n//# sourceURL=testing_sourceURL.js")

//# sourceURL • Must be used from JavaScript eval • Supported
in IE11 / Firefox and Chrome • Easily backported into Asset Pipeline

Awesome fast debugging for Rails Shout out to Robin Ward
for building this

sourceURL performance • 900 js assets • First Paint 1.4 seconds
(was 30 seconds) • Dom loaded 1.7 seconds (was 60 seconds) • High latency friendly • Can be easily added to Asset Pipeline

Choose your own adventure • Try out other frameworks and
gems • Find your boOlenecks • Have fun • Experiment

We can make our applica4ons faster

We can make our frameworks consume less memory

We have the tooling

Off The Rails

Off The Rails

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