feat: add connection waiting statistics (#2804)

Co-authored-by: ofekshenawa <[email protected]>

Author: lzakharov

internal/pool/pool.go

@@ -33,9 +33,11 @@ var timers = sync.Pool{
 
 // Stats contains pool state information and accumulated stats.
 type Stats struct {
-	Hits     uint32 // number of times free connection was found in the pool
-	Misses   uint32 // number of times free connection was NOT found in the pool
-	Timeouts uint32 // number of times a wait timeout occurred
+	Hits           uint32 // number of times free connection was found in the pool
+	Misses         uint32 // number of times free connection was NOT found in the pool
+	Timeouts       uint32 // number of times a wait timeout occurred
+	WaitCount      uint32 // number of times a connection was waited
+	WaitDurationNs int64  // total time spent for waiting a connection in nanoseconds
 
 	TotalConns uint32 // number of total connections in the pool
 	IdleConns  uint32 // number of idle connections in the pool
@@ -90,7 +92,8 @@ type ConnPool struct {
 	poolSize     int
 	idleConnsLen int
 
-	stats Stats
+	stats          Stats
+	waitDurationNs atomic.Int64
 
 	_closed uint32 // atomic
 }
@@ -320,6 +323,7 @@ func (p *ConnPool) waitTurn(ctx context.Context) error {
 	default:
 	}
 
+	start := time.Now()
 	timer := timers.Get().(*time.Timer)
 	timer.Reset(p.cfg.PoolTimeout)
 
@@ -331,6 +335,8 @@ func (p *ConnPool) waitTurn(ctx context.Context) error {
 		timers.Put(timer)
 		return ctx.Err()
 	case p.queue <- struct{}{}:
+		p.waitDurationNs.Add(time.Since(start).Nanoseconds())
+		atomic.AddUint32(&p.stats.WaitCount, 1)
 		if !timer.Stop() {
 			<-timer.C
 		}
@@ -457,9 +463,11 @@ func (p *ConnPool) IdleLen() int {
 
 func (p *ConnPool) Stats() *Stats {
 	return &Stats{
-		Hits:     atomic.LoadUint32(&p.stats.Hits),
-		Misses:   atomic.LoadUint32(&p.stats.Misses),
-		Timeouts: atomic.LoadUint32(&p.stats.Timeouts),
+		Hits:           atomic.LoadUint32(&p.stats.Hits),
+		Misses:         atomic.LoadUint32(&p.stats.Misses),
+		Timeouts:       atomic.LoadUint32(&p.stats.Timeouts),
+		WaitCount:      atomic.LoadUint32(&p.stats.WaitCount),
+		WaitDurationNs: p.waitDurationNs.Load(),
 
 		TotalConns: uint32(p.Len()),
 		IdleConns:  uint32(p.IdleLen()),

internal/pool/pool_test.go

@@ -59,12 +59,14 @@ var _ = Describe("ConnPool", func() {
 		time.Sleep(time.Second)
 
 		Expect(connPool.Stats()).To(Equal(&pool.Stats{
-			Hits:       0,
-			Misses:     0,
-			Timeouts:   0,
-			TotalConns: 0,
-			IdleConns:  0,
-			StaleConns: 0,
+			Hits:           0,
+			Misses:         0,
+			Timeouts:       0,
+			WaitCount:      0,
+			WaitDurationNs: 0,
+			TotalConns:     0,
+			IdleConns:      0,
+			StaleConns:     0,
 		}))
 	})
 
@@ -358,4 +360,31 @@ var _ = Describe("race", func() {
 		Expect(stats.IdleConns).To(Equal(uint32(0)))
 		Expect(stats.TotalConns).To(Equal(uint32(opt.PoolSize)))
 	})
+
+	It("wait", func() {
+		opt := &pool.Options{
+			Dialer: func(ctx context.Context) (net.Conn, error) {
+				return &net.TCPConn{}, nil
+			},
+			PoolSize:    1,
+			PoolTimeout: 3 * time.Second,
+		}
+		p := pool.NewConnPool(opt)
+
+		wait := make(chan struct{})
+		conn, _ := p.Get(ctx)
+		go func() {
+			_, _ = p.Get(ctx)
+			wait <- struct{}{}
+		}()
+		time.Sleep(time.Second)
+		p.Put(ctx, conn)
+		<-wait
+
+		stats := p.Stats()
+		Expect(stats.IdleConns).To(Equal(uint32(0)))
+		Expect(stats.TotalConns).To(Equal(uint32(1)))
+		Expect(stats.WaitCount).To(Equal(uint32(1)))
+		Expect(stats.WaitDurationNs).To(BeNumerically("~", time.Second.Nanoseconds(), 100*time.Millisecond.Nanoseconds()))
+	})
 })