Improve pool Acquire / Release performance

Release was using a goroutine every time. Now it only starts a goroutine
when doing something that may take a while. (Destroy and afterRelease)

bench_test.go

@@ -26,7 +26,7 @@ func BenchmarkMinimalPreparedSelect(b *testing.B) {
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		err = conn.QueryRow(context.Background(), "ps1", int64(i)).Scan(&n)
+		err = conn.QueryRow(context.Background(), "ps1", i).Scan(&n)
 		if err != nil {
 			b.Fatal(err)
 		}
@@ -37,6 +37,41 @@ func BenchmarkMinimalPreparedSelect(b *testing.B) {
 	}
 }
 
+func BenchmarkMinimalPgConnPreparedSelect(b *testing.B) {
+	conn := mustConnect(b, mustParseConfig(b, os.Getenv("PGX_TEST_DATABASE")))
+	defer closeConn(b, conn)
+
+	pgConn := conn.PgConn()
+
+	_, err := pgConn.Prepare(context.Background(), "ps1", "select $1::int8", nil)
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	encodedBytes := make([]byte, 8)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+
+		rr := pgConn.ExecPrepared(context.Background(), "ps1", [][]byte{encodedBytes}, []int16{1}, []int16{1})
+		if err != nil {
+			b.Fatal(err)
+		}
+
+		for rr.NextRow() {
+			for i := range rr.Values() {
+				if bytes.Compare(rr.Values()[0], encodedBytes) != 0 {
+					b.Fatalf("unexpected values: %s %s", rr.Values()[i], encodedBytes)
+				}
+			}
+		}
+		_, err = rr.Close()
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
 func BenchmarkPointerPointerWithNullValues(b *testing.B) {
 	conn := mustConnect(b, mustParseConfig(b, os.Getenv("PGX_TEST_DATABASE")))
 	defer closeConn(b, conn)

pool/bench_test.go

@@ -10,6 +10,21 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func BenchmarkAcquireAndRelease(b *testing.B) {
+	pool, err := pool.Connect(context.Background(), os.Getenv("PGX_TEST_DATABASE"))
+	require.NoError(b, err)
+	defer pool.Close()
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		c, err := pool.Acquire(context.Background())
+		if err != nil {
+			b.Fatal(err)
+		}
+		c.Release()
+	}
+}
+
 func BenchmarkMinimalPreparedSelectBaseline(b *testing.B) {
 	config, err := pool.ParseConfig(os.Getenv("PGX_TEST_DATABASE"))
 	require.NoError(b, err)

pool/conn.go

@@ -26,14 +26,19 @@ func (c *Conn) Release() {
 	res := c.res
 	c.res = nil
 
-	go func() {
-		now := time.Now()
-		if !conn.IsAlive() || conn.PgConn().TxStatus != 'I' || (now.Sub(res.CreationTime()) > c.p.maxConnLifetime) {
-			res.Destroy()
-			return
-		}
+	now := time.Now()
+	if !conn.IsAlive() || conn.PgConn().TxStatus != 'I' || (now.Sub(res.CreationTime()) > c.p.maxConnLifetime) {
+		res.Destroy()
+		return
+	}
 
-		if c.p.afterRelease == nil || c.p.afterRelease(conn) {
+	if c.p.afterRelease == nil {
+		res.Release()
+		return
+	}
+
+	go func() {
+		if c.p.afterRelease(conn) {
 			res.Release()
 		} else {
 			res.Destroy()
@@ -66,7 +71,7 @@ func (c *Conn) Begin(ctx context.Context, txOptions *pgx.TxOptions) (*pgx.Tx, er
 }
 
 func (c *Conn) Conn() *pgx.Conn {
-	return c.res.Value().(*connResource).conn
+	return c.connResource().conn
 }
 
 func (c *Conn) connResource() *connResource {

pool/pool.go

@@ -150,9 +150,11 @@ func ConnectConfig(ctx context.Context, config *Config) (*Pool, error) {
 			return cr, nil
 		},
 		func(value interface{}) {
-			ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
-			value.(*connResource).conn.Close(ctx)
-			cancel()
+			go func() {
+				ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+				value.(*connResource).conn.Close(ctx)
+				cancel()
+			}()
 		},
 		config.MaxConns,
 	)