Default MaxIdleConnections to 2 when unset

net2/base_connection_pool.go

@@ -10,6 +10,9 @@ import (
 
 const defaultDialTimeout = 1 * time.Second
 
+// Default idle pool size when ConnectionOptions.MaxIdleConnections is unset.
+const defaultMaxIdleConnections uint32 = 2
+
 func defaultDialFunc(network string, address string) (net.Conn, error) {
 	return net.DialTimeout(network, address, defaultDialTimeout)
 }
@@ -53,9 +56,14 @@ func newBaseConnectionPool(
 		return handle.(net.Conn).Close()
 	}
 
+	maxIdle := options.MaxIdleConnections
+	if maxIdle == 0 {
+		maxIdle = defaultMaxIdleConnections
+	}
+
 	poolOptions := rp.Options{
 		MaxActiveHandles:   options.MaxActiveConnections,
-		MaxIdleHandles:     options.MaxIdleConnections,
+		MaxIdleHandles:     maxIdle,
 		MaxIdleTime:        options.MaxIdleTime,
 		OpenMaxConcurrency: options.DialMaxConcurrency,
 		Open:               openFunc,

net2/base_connection_pool_test.go

@@ -288,6 +288,30 @@ func (s *BaseConnectionPoolSuite) TestMaxActiveConnections(c *C) {
 	c.Assert(pool.NumActive(), Equals, int32(0))
 }
 
+func (s *BaseConnectionPoolSuite) TestDefaultMaxIdleConnections(c *C) {
+	// Unset MaxIdleConnections used to mean keep zero idle handles, which
+	// forced a dial on every Get. Zero now applies a small default idle size.
+	dialer := fakeDialer{}
+	mockClock := time2.MockClock{}
+
+	options := ConnectionOptions{
+		Dial:    dialer.FakeDial,
+		NowFunc: mockClock.Now,
+	}
+	pool := NewSimpleConnectionPool(options)
+	pool.Register("foo", "bar")
+
+	c1, err := pool.Get("foo", "bar")
+	c.Assert(err, IsNil)
+	err = c1.ReleaseConnection()
+	c.Assert(err, IsNil)
+	c.Assert(pool.NumIdle(), Equals, 1)
+
+	c2, err := pool.Get("foo", "bar")
+	c.Assert(err, IsNil)
+	c.Assert(SameConnection(c1, c2), IsTrue)
+}
+
 func (s *BaseConnectionPoolSuite) TestMaxIdleConnections(c *C) {
 	dialer := fakeDialer{}
 	mockClock := time2.MockClock{}

net2/connection_pool.go

@@ -12,7 +12,8 @@ type ConnectionOptions struct {
 	MaxActiveConnections int32
 
 	// The maximum number of idle connections per host that are kept alive by
-	// the connection pool.
+	// the connection pool. When unset (zero), a default of 2 is used so the
+	// Go zero value does not disable idle reuse and force a dial on every Get.
 	MaxIdleConnections uint32
 
 	// The maximum amount of time an idle connection can alive (if specified).