The 1990s Called. They Want Their Code Back.

The 1990s Called. They Want Their
Code Back.
5 Ways Your Code is Stuck in the 90s
3 Mar 2015
Jonathan Oliver

$ whoami
@jonathan_oliver
http://jonathanoliver.com
http://github.com/joliver
http://keybase.com/joliver
Distributed Podcast
Chief SmartyPants, SmartyStreets

Overview
Disclaimers
Why Go Exists
#1 Implicit messaging
#2 Complex Threading
#3 RPC Everywhere
#4 GC
#5 Logging
Conclusion

Caveats: But, but, but...
Your mileage may vary
Don't apply blindly or wholesale
Sharp knife

Our experience
C# on Windows vs Go on Linux (512 req/s)
hdrhistogram.org

C# Windows vs Golang Linux at 4096 req/s
hdrhistogram.org

C# Windows vs Golang Linux at 8192 req/s
hdrhistogram.org

Why Go Exists
(The real reason)
Compile times?
Multi-core, networked systems

1990ism #1: Implicit Messaging

Hint Dropping Fallacy
If you have to ask, it doesn't mean as much
If you really loved me, you'd know

Implicit Messaging: PHP
<?php
$sql = 'UPDATE Users SET ' +
'firstname = ' $_GET['firstname'] + ','+
'lastname = ' $_GET['lastname'] + ','+
'phone = ' $_GET['phone'] + ','+
'password = ' hash($_GET['password']) + ','+
'WHERE id=' + $_GET['id'];
mysql_query($sql, $connection) or die("Couldn't execute query.");
?>

Implicit Messaging: Go
Where does HTTP stop and the application start?
func implicit(response http.ResponseWriter, request *http.Request) {
query := request.URL.Query()
statement := `UPDATE Users
SET firstname = '%s',
lastname = '%s',
phone = '%s',
password='%s'
WHERE id = %s;`
sql.Execute(statement,
query.Get("firstname"),
query.Get("lastname"),
query.Get("phone"),
hashAndSalt(query.Get("password")),
query.Get("id"))
response.WriteHeader(200)
}

Implicit Messaging: Boundaries
HTTP bleeds all over the application
.NET: System.Web.HttpContext.Current.Request...

Implicit Messaging: Intention?
I know! I'll use a DTO that corresponds to my table!
Hello, Ruby on Rails / Active Record
type User struct {
ID int
FirstName string
LastName string
Phone string
Password []byte
}
Staring at the table salt: implicit or inferred understanding

type User struct {
ID int
FirstName string
LastName string
Phone string
Password []byte
}

Solution #1: Explicit Contracts

Application Protocols 101:
HTTP: Hypertext Transfer Protocol
SMTP: Simple Mail Transfer Protocol
FTP: File Transfer Protocol (control channel, port 21)
Transfering what?

Messages!
Review HTTP, SMTP, etc. RFC speciﬁcations
e.g. HTTP message body, HTTP message headers, etc.
HTTP, SMTP, etc. encapsulate a message

DTOs: What Are Your Intentions?
Implicit / Inferred (Active Record)
type User struct {
ID int
FirstName string
LastName string
Phone string
Password []byte
}
Explicit
type ChangePasswordCommand struct {
UserID int
NewPassword string
NewPasswordConfirmed string
OldPassword string
}

Messaging How-To
HTTP values into message struct
URL+VERB determines message type
Query String
Form Values
Deserialize body or HTTP 400

Messaging How-To (continued)
HTTP is an interface to application
Push message into application layer
Additional interfaces, e.g. SMTP, AMQP, CLI, etc.

1990ism #2: Complex Threading Code

Goroutine per HTTP request
Terrible for shared state like:
Incrementing a counter
Modify a map
Updating object references

Goroutine per request = manual synchronization of shared state
Go doesn't save us from synchronization code
go keyword can make things harder
package main
import "fmt"
import "time"
func main() {
for i := 0; i < 4; i++ {
go func() {
fmt.Println(i) // bad closure
}()
}
time.Sleep(time.Millisecond)
}

Solution #2: In-process "microservices" (Actors)

Actor Example:
// uncontended state
func listen() {
for message := this.incomingChannel {
// single-threaded with synchronization primitives
counter++
map[message.UserID]++
// additional message processing code
this.outgoingChannel <- message
}
}
The Unix Way: Small & Composable
Message In, Message Out: Easy Testing
Pipes and Filters
Marshal to external process

Break Apart Stateful and Stateless Operations
func (this CounterPhase) listen() {
for message := this.incomingChannel {
counter++ // stateful; single-threaded with no sync code
message.Sequence = counter
this.outgoingChannel <- message // outgoing to process phase
}
}
func (this ProcessPhase) listen() {
// can be stateless because state was assigned in previous phase
for i := 0; i < runtime.NumCPU(); i++ {
go func() {
for message := this.incomingChannel { // incoming from counter phase
// process message (CPU/network operations)
this.outgoingChannel <- message
}
}()
}
}

HTTP RPC
Block the caller until the work is done
func handle(w http.ResponseWriter, r *http.Request) {
var wg sync.WaitGroup
wg.Add(1)
query := r.URL.Query()
this.application <- ChangePasswordCommand{
UserID: cookie.Get("user-id"),
OldPassword: query.Get("old-password"),
NewPassword: query.Get("new-password"),
NewPasswordConfirmed: query.Get("new-password-confirmed"),
WaitGroup: &wg,
}
wg.Wait()
// return result of application
}

Queues and Natural Backpressure
Typical performance characteristics at 90% vs 99% utilization

1990ism #3: Remote Procedure Call Everywhere

Fallacies of Distributed Computing
The Network is Reliable
Latency is Zero

Typical Application Behavior (Transaction Script)
Opens a DB connection
Start a transaction
Execute DB operation(s)
Other operations? (Send email, etc.)
Commit transaction
Wash, rinse, repeat
What could possibly go wrong?

Fragile RPC
Per business demands, we add "one more thing", e.g. email, etc.
When network is down, lots of things break
Bill credit card, send email, etc.
Netﬂix architecture

Solution #3: Actors (again) + Embrace Failure

Simple Retry Code
import "time"
func listen() {
// simple retry
for message := range this.incoming {
for attempt := 0; attempt < 5; attempt++ {
if err := emailReceipt(message); err != nil {
time.Sleep(time.Second * 30)
continue
}
}
}
}

BONUS POINTS: Simple Batching
Story: Moving one box at a time
func listen() {
for message := range this.incoming {
addToUnitOfWork(message)
if len(this.incoming) == 0 || len(batch) >= 100 {
commit()
newTransaction()
}
}
}
1-2 order of magnitude performance increase

1990ism #4: Abuse Garbage Collection

Primitive, mark-and-sweep implementation
But getting better...
Java and .NET
pointers
maps
strings
slices

The 1990s Called. They Want Their Code Back.

GC Pause Latency and You
Are 500 ms GC pauses okay?
How about 5 seconds?
What is latency costing you?

Solution #4: Understanding GC Behavior

Measure, measure, measure
Avoid pointers (where possible)
Preallocate and re-use structures (where possible)
My bug report (issue #9477) & maps of structs (v1.5)
Keep byte slices oﬀ heap (where possible)
Size of the heap

1990ism #5: Logging Is Suﬃcient

Logging is awesome, but very "trees" focused
Stored?
Where?
How long?
Who analyzes and when?
Calls to log.Print result in blocking syscalls that yield the goroutine
Hard to make blocking/yielding calls

Solution #5: Metrics, Metrics, Everywhere

Business Value (Coda Hale: Metrics, Metrics, Everywhere)
Business value is anything which makes people more likely to give us money

We want to generate more business value

Our code generates business value when it runs—NOT when we write it.

We need to make better decisions about our code

We need to know what our code does when it runs

We can’t do this unless we MEASURE it

Our mental model of our code is not our code.

Example: This code can’t possibly work; it works.

Example: This code can’t fail; it fails

Example: Do these changes make things faster?

We can’t know until we MEASURE it

We improve our mental model by measuring what our code DOES

A better mental model makes us better at deciding what to do—at generating business
value

Understanding Your Application
Instrument your application (metrics)
Understand how it's being used
Understand the pathways that are taken (counters)
Understand how much (disk/memory/etc) you have left (gauges)

Service Providers
Librato (http://github.com/smartystreets/metrics)
Boundary
Datadog

Go != other languages
Work with concurrency primitives
Explicit messages
Message pipelines ("actors")
Simple logic, simple code

Thank you
3 Mar 2015
Jonathan Oliver
@jonathan_oliver(http://twitter.com/jonathan_oliver)
http://jonathanoliver.com(http://jonathanoliver.com)
http://github.com/joliver(http://github.com/joliver)
http://keybase.com/joliver(http://keybase.com/joliver)
Distributed Podcast
Chief SmartyPants, SmartyStreets

The 1990s Called. They Want Their Code Back.

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