InDrive - 1

• Tell about the map go/maps
• Can you read from a map in multiple threads? go/maps
• What is sync.Map? go/sync
• Have you had to run a profiler in production? hr-behavioral/about-you
• What happens in the code when you write go and a goroutine? go/concurrency
• What kinds of channels are there? go/channels
• What types of memory are there in Go? go/memory-gc
• What memory does the garbage collector work with? go/memory-gc
• What will this output? go/puzzles

Задача: (код без описания) go/basics

func main() {
  var strData string
  for i := 0; i < 10; i++ {
    strData += fmt.Sprintf("%d ", i)
  }
  fmt.Println(strData)
}

• What will this output? go/puzzles

Задача: (код без описания) go/basics

func main() {
  defer fmt.Println(1)
  time.Sleep(1 * time.Second)
  go fmt.Println(2)
  go fmt.Println(3)
}

• Is defer always called? go/errors-panic
• What will this output? go/puzzles

Задача: (код без описания) go/basics

func main() {
  ctx, _ := context.WithTimeout(context.Background(), 3*time.Second)
  time.Sleep(2950 * time.Millisecond)
  doDbRequest(ctx)
}

func doDbRequest(ctx context.Context) {
  newCtx, _ := context.WithTimeout(ctx, 10*time.Second)
  timer := time.NewTimer(1 * time.Second)

  select {
  case <-newCtx.Done():
    fmt.Println("Timeout ")
  case <-timer.C:
    fmt.Println("Request Done ")
  }
}

• What will this output? go/puzzles

Задача: (код без описания) go/basics

var counter = 0

func main() {
  for i := 0; i < 10; i++ {
    go func() { counter++ }()
  }

  time.Sleep(2 * time.Second)
  fmt.Println(counter)
}

• There are three goroutines where run is blocked. How to make the steady function simultaneously unblock all three runs? go/concurrency

Задача: (код без описания) go/basics

func runnerStart() {
  go ready()
  go ready()
  go ready()

  steady()
  // ensure they start running after the call, simultaneously
}

func steady() {
  // write
}

func ready() {
  // wait for steady call
  run()
}

• Complete the code so that the task runs asynchronously with a limit on the number of simultaneous requests go/concurrency

Задача: (код без описания) go/basics

func main() {
  // Make this code asynchronous with controlled parallel request numbers
  for _, val := range getData() {
    if !checkDomain(val) {
      fmt.Printf("%s is bad \n ", val)
    }
  }
}

func getData() []string {
  return []string{"1.test ", "2.test " /*...*/, "1000.test "}
}

func checkDomain(host string) bool {
  return true
}

• Merge two sorted arrays go/slices-arrays

Задача: (код без описания) go/basics

func main() {
  // a, b - sorted slices
  var a = []int{1, 5, 6, 18, 99}
  var b = []int{2, 4, 9, 11}

  fmt.Println(mergeSorted(a, b))
}

func mergeSorted(a []int, b []int) {
  // write
}

• There is a method that iterates through all records from a table by increasing the offset. What problems do you see? sql/query-optimization

Задача: (код без описания) sql/general

select*from news where category_id =1 limit 10 offset 100;

• Question about indexes sql/indexes
• What does B in B-Tree index stand for sql/indexes
• Question about escaping in SQL queries sql/general
• Question about locking in SQL sql/general
• Explain ACID sql/transactions
• Have you heard of deadlocks in databases? go/sync
• What is sharding? sql/replication-scaling

Задача: Describe methods, speed up data retrieval. The task depends on the dialogue. algorithms/data-structures

// building a weather app. Getting weather forecast by country.
// Data updates come infrequently relative to reads and irregularly.
// A 2-hour data lag is acceptable
// The DB works poorly and slowly, 700-800ms

type database interface {
  get(ctx context.Context, key string) (string, error)
  save(ctx context.Context, key, value string) error
}

type Repository struct {
  db database
}

func (r *Repository) Get(ctx context.Context, key string) (string, error) {
  return r.db.get(ctx, key)
}

func (r *Repository) Save(ctx context.Context, key, value string) error {
  return r.db.save(ctx, key, value)
}