CodeCampIasi25Oct2014

1. The Sad ˝
Story ˝
Of the Server ˝
that Tries to ˝
Please Everyone
Iulian Dogariu
CodeCamp 25 Oct 2014

3. Lil' server
object Tickets extends Controller {
def book(eventId: Int, count: Int) = Action {
val bookings: Seq[Booking] =
TicketsRepository.bookForEvent(eventId, count)
Ok(s"Thank you! These are your bookings " +
bookings.mkString("n"))
}
}

4. Lil' server
object Tickets extends Controller {
def book(eventId: Int, count: Int) = Action {
val bookings: Seq[Booking] =
TicketsRepository.bookForEvent(eventId, count)
Ok(s"Thank you! These are your bookings " +
bookings.mkString("n"))
}
}

5. More than a lil'
def bookForEvent(eventId: Int, count: Int): Seq[Booking] = {
DB.withTransaction { implicit c =>
val numAvailableTickets: Int = SQL(
"SELECT num_free FROM tickets WHERE event_id={eventId}").
on("eventId" -> eventId).as(SqlParser.int("num_free").single)
(0 to count).map { _ =>
val bookingId: Option[Long] = SQL(
"INSERT INTO bookings(event_id)" +
" VALUES({eventId})").on('eventId -> eventId).executeInsert()
Booking(bookingId, eventId)
}
}
}

6. More than a lil'

7. How bad is it?
Normal CPU instruction
Fetch from RAM
Disk seek
Ping from Iași to Bucharest
Ping from Iași to USA
0.5 nsec
120 nsec
10 msec
30 msec
130 msec

8. No, really
Normal CPU instruction
Fetch from RAM
Disk seek
Ping from Iași to Bucharest
Ping from Iași to USA
1 sec
4 min
7.5 Months
2 Years
6 Years

9. Back to the lil' server

10. Back to the lil' server

11. Back to the lil' server

13. What does the user see?

15. If I only knew...
• I'd go somewhere else!

16. Show me the bottleneck

17. Queues and messages
bookingActor ! NewBookingCommand(1, 2)
def receive = {
case BookingSucceeded(eventId, bookings) =>
println(s"Thank you!" + bookings.mkString("n"))
}
class BookingActor extends Actor {
def receive = {
case NewBookingCommand(eventId, ct) =>
val bookings = TicketsRepository.bookForEvent(eventId, ct)
sender ! BookingSucceeded(eventId, bookings)
}
}

18. One small step

19. Pulling work
GIMME WORK!!

20. WIP

21. The math of WIP

23. Push back

24. Push back

25. Reactive streams

26. Reactive streams

27. val bookingFlow =
Flow[NewBookingCommand].map { command =>
val bookings = TicketsRepository.
bookForEvent(command.eventId, command.count)
BookingSucceeded(
command.eventId, bookings)
}

28. val in = ThunkTap[NewBookingCommand] {
// Flood with requests
Some(NewBookingCommand(1, 2))
}
val out = ForeachDrain[BookingSucceeded] {
case BookingSucceeded(eventId, bookings) =>
println(s"Thank you!" + bookings.mkString("n"))
}

29. FlowGraph { implicit b =>
in ~> bookingFlow ~> out
}.run()
Altogether now
Tap Flow
Drain

30. Recap
• Do you really know what's slow in your code?
• Queues make bottlenecks obvious
• If you can't serve me, tell me so ("Agree to Start")
• Because people pleasers end up disappointing
everyone equally :-)

31. The Soup Nazi problem

33. Q & A ?

34. Thank You, Come Again
And please fill in the evaluation form :-)