High-Concurrency Performance Fix | Dataford Interview Questions

Your question is High-Concurrency Performance Fix. Take a moment with it on the right.

Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).

Problem

You're a backend engineer at Aubay Spain, staffed on a client project for a concert ticketing platform. This Go snippet reserves seats when a booking burst comes in right as tickets go on sale, and under real load it panics and oversells seats.

package main

import "fmt"
import "sync"
import "time"

var seatsRemaining = map[string]int{
	"A1": 5,
	"A2": 3,
}

func reserveSeat(seatID string, wg *sync.WaitGroup) {
	defer wg.Done()

	remaining := seatsRemaining[seatID]
	time.Sleep(10 * time.Millisecond)

	if remaining > 0 {
		seatsRemaining[seatID] = remaining - 1
		fmt.Println("reserved", seatID)
	} else {
		fmt.Println("sold out", seatID)
	}
}

func handleBookingBurst(requests []string) {
	var wg sync.WaitGroup

	for _, seatID := range requests {
		wg.Add(1)
		go reserveSeat(seatID, &wg)
	}

	wg.Wait()
}

Fix this snippet to be correct and to perform well under a high-concurrency burst of booking requests. Explain what you would change and why, without needing to submit a full patch.

Your question is High-Concurrency Performance Fix. Take a moment with it on the right.

Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).

package main

import "fmt"
import "sync"
import "time"

var seatsRemaining = map[string]int{
	"A1": 5,
	"A2": 3,
}

func reserveSeat(seatID string, wg *sync.WaitGroup) {
	defer wg.Done()

	remaining := seatsRemaining[seatID]
	time.Sleep(10 * time.Millisecond)

	if remaining > 0 {
		seatsRemaining[seatID] = remaining - 1
		fmt.Println("reserved", seatID)
	} else {
		fmt.Println("sold out", seatID)
	}
}

func handleBookingBurst(requests []string) {
	var wg sync.WaitGroup

	for _, seatID := range requests {
		wg.Add(1)
		go reserveSeat(seatID, &wg)
	}

	wg.Wait()
}

Fix this snippet to be correct and to perform well under a high-concurrency burst of booking requests. Explain what you would change and why, without needing to submit a full patch.