database/sql: allow Stmt Query and Exec methods to open a new conn

Query and Exec functions on DB first attempt to get a cached
connection before requesting the connection pool to ignore
the cache and get a new connection. This change aligns Stmt to
that behavior as well.

Fixes #20433

Change-Id: Idda5f61927289d7ad0882effa3a50ffc9efd88e6
Reviewed-on: https://go-review.googlesource.com/43790
Run-TryBot: Daniel Theophanes <kardianos@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/database/sql/sql.go

@@ -2029,8 +2029,12 @@ func (s *Stmt) ExecContext(ctx context.Context, args ...interface{}) (Result, er
 	defer s.closemu.RUnlock()
 
 	var res Result
-	for i := 0; i < maxBadConnRetries; i++ {
-		dc, releaseConn, ds, err := s.connStmt(ctx)
+	strategy := cachedOrNewConn
+	for i := 0; i < maxBadConnRetries+1; i++ {
+		if i == maxBadConnRetries {
+			strategy = alwaysNewConn
+		}
+		dc, releaseConn, ds, err := s.connStmt(ctx, strategy)
 		if err != nil {
 			if err == driver.ErrBadConn {
 				continue
@@ -2098,7 +2102,7 @@ func (s *Stmt) removeClosedStmtLocked() {
 // connStmt returns a free driver connection on which to execute the
 // statement, a function to call to release the connection, and a
 // statement bound to that connection.
-func (s *Stmt) connStmt(ctx context.Context) (ci *driverConn, releaseConn func(error), ds *driverStmt, err error) {
+func (s *Stmt) connStmt(ctx context.Context, strategy connReuseStrategy) (ci *driverConn, releaseConn func(error), ds *driverStmt, err error) {
 	if err = s.stickyErr; err != nil {
 		return
 	}
@@ -2124,7 +2128,7 @@ func (s *Stmt) connStmt(ctx context.Context) (ci *driverConn, releaseConn func(e
 	s.removeClosedStmtLocked()
 	s.mu.Unlock()
 
-	dc, err := s.db.conn(ctx, cachedOrNewConn)
+	dc, err := s.db.conn(ctx, strategy)
 	if err != nil {
 		return nil, nil, nil, err
 	}
@@ -2171,8 +2175,12 @@ func (s *Stmt) QueryContext(ctx context.Context, args ...interface{}) (*Rows, er
 	defer s.closemu.RUnlock()
 
 	var rowsi driver.Rows
-	for i := 0; i < maxBadConnRetries; i++ {
-		dc, releaseConn, ds, err := s.connStmt(ctx)
+	strategy := cachedOrNewConn
+	for i := 0; i < maxBadConnRetries+1; i++ {
+		if i == maxBadConnRetries {
+			strategy = alwaysNewConn
+		}
+		dc, releaseConn, ds, err := s.connStmt(ctx, strategy)
 		if err != nil {
 			if err == driver.ErrBadConn {
 				continue

src/database/sql/sql_test.go

@@ -2334,9 +2334,13 @@ func TestStmtCloseOrder(t *testing.T) {
 // Test cases where there's more than maxBadConnRetries bad connections in the
 // pool (issue 8834)
 func TestManyErrBadConn(t *testing.T) {
-	manyErrBadConnSetup := func() *DB {
+	manyErrBadConnSetup := func(first ...func(db *DB)) *DB {
 		db := newTestDB(t, "people")
 
+		for _, f := range first {
+			f(db)
+		}
+
 		nconn := maxBadConnRetries + 1
 		db.SetMaxIdleConns(nconn)
 		db.SetMaxOpenConns(nconn)
@@ -2405,6 +2409,41 @@ func TestManyErrBadConn(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	// Stmt.Exec
+	db = manyErrBadConnSetup(func(db *DB) {
+		stmt, err = db.Prepare("INSERT|people|name=Julia,age=19")
+		if err != nil {
+			t.Fatal(err)
+		}
+	})
+	defer closeDB(t, db)
+	_, err = stmt.Exec()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err = stmt.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	// Stmt.Query
+	db = manyErrBadConnSetup(func(db *DB) {
+		stmt, err = db.Prepare("SELECT|people|age,name|")
+		if err != nil {
+			t.Fatal(err)
+		}
+	})
+	defer closeDB(t, db)
+	rows, err = stmt.Query()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err = rows.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if err = stmt.Close(); err != nil {
+		t.Fatal(err)
+	}
+
 	// Conn
 	db = manyErrBadConnSetup()
 	defer closeDB(t, db)