Allow ConnPool to have MaxConnections of 1

conn_pool.go

@@ -37,8 +37,8 @@ func NewConnPool(config ConnPoolConfig) (p *ConnPool, err error) {
 	if p.maxConnections == 0 {
 		p.maxConnections = 5
 	}
-	if p.maxConnections < 2 {
-		return nil, errors.New("MaxConnections must be at least 2")
+	if p.maxConnections < 1 {
+		return nil, errors.New("MaxConnections must be at least 1")
 	}
 
 	p.afterConnect = config.AfterConnect

conn_pool_test.go

@@ -67,20 +67,6 @@ func TestNewConnPoolDefaultsTo5MaxConnections(t *testing.T) {
 	}
 }
 
-func TestNewConnPoolMaxConnectionsCannotBeLessThan2(t *testing.T) {
-	t.Parallel()
-
-	config := pgx.ConnPoolConfig{ConnConfig: *defaultConnConfig, MaxConnections: 1}
-	pool, err := pgx.NewConnPool(config)
-	if err == nil {
-		pool.Close()
-		t.Fatal(`Expected NewConnPool to fail with "MaxConnections must be at least 2" error, but it succeeded`)
-	}
-	if err.Error() != "MaxConnections must be at least 2" {
-		t.Fatalf(`Expected NewConnPool to fail with "MaxConnections must be at least 2" error, but it failed with %v`, err)
-	}
-}
-
 func TestPoolAcquireAndReleaseCycle(t *testing.T) {
 	t.Parallel()
 

stdlib/sql.go

@@ -109,6 +109,8 @@ func (d *Driver) Open(name string) (driver.Conn, error) {
 // *sql.DB and typecasting to *stdlib.Driver a reference to the pgx.ConnPool can
 // be reaquired later. This allows fast paths targeting pgx to be used while
 // still maintaining compatibility with other databases and drivers.
+//
+// pool connection size must be at least 2.
 func OpenFromConnPool(pool *pgx.ConnPool) (*sql.DB, error) {
 	d := &Driver{Pool: pool}
 	name := fmt.Sprintf("pgx-%d", openFromConnPoolCount)
@@ -126,6 +128,10 @@ func OpenFromConnPool(pool *pgx.ConnPool) (*sql.DB, error) {
 	// that would mean that prepared statements would be lost (which kills
 	// performance if the prepared statements constantly have to be reprepared)
 	stat := pool.Stat()
+
+	if stat.MaxConnections <= 2 {
+		return nil, errors.New("pool connection size must be at least 2")
+	}
 	db.SetMaxIdleConns(stat.MaxConnections - 2)
 	db.SetMaxOpenConns(stat.MaxConnections)