issue-708: Set lock_wait_timeout to SetReadOnly

clustering/operations.go

@@ -151,12 +151,31 @@ func (p *managerProcess) switchover(ctx context.Context, ss *StatusSet) error {
 	log.Info("begin switchover the primary", "current", ss.Primary, "next", ss.Candidate)
 
 	pdb := ss.DBOps[ss.Primary]
-	if err := pdb.SetReadOnly(ctx, true); err != nil {
-		return fmt.Errorf("failed to make instance %d read-only: %w", ss.Primary, err)
+
+	// SetReadOnly waits for a running DML.
+	// Therefore, if it waits for a long time, deleteGracePeriodSeconds may be reached.
+	// To avoid this, set lock_wait_timeout to a short time temporarily.
+	// If SetReadOnly fails, kill all processes and retry.
+	succeeded := false
+	if err := pdb.SetSessionLockWaitTimeout(ctx, 15); err != nil {
+		return fmt.Errorf("failed to set lock_wait_timeout: %w", err)
+	}
+	for i := 0; i < 2; i++ {
+		if err := pdb.SetReadOnly(ctx, true); err != nil {
+			log.Error(err, "failed to set read-only mode", "instance", ss.Primary)
+		} else {
+			succeeded = true
+		}
+		time.Sleep(100 * time.Millisecond)
+		if err := pdb.KillConnections(ctx); err != nil {
+			return fmt.Errorf("failed to kill connections in instance %d: %w", ss.Primary, err)
+		}
+		if succeeded {
+			break
+		}
 	}
-	time.Sleep(100 * time.Millisecond)
-	if err := pdb.KillConnections(ctx); err != nil {
-		return fmt.Errorf("failed to kill connections in instance %d: %w", ss.Primary, err)
+	if !succeeded {
+		return fmt.Errorf("failed to set read-only mode in instance %d", ss.Primary)
 	}
 	pst, err := pdb.GetStatus(ctx)
 	if err != nil {

pkg/dbop/nop.go

@@ -51,6 +51,10 @@ func (o NopOperator) WaitForGTID(ctx context.Context, gtidSet string, timeoutSec
 	return ErrNop
 }
 
+func (o NopOperator) SetSessionLockWaitTimeout(ctx context.Context, timeoutSeconds int) error {
+	return ErrNop
+}
+
 func (o NopOperator) SetReadOnly(context.Context, bool) error {
 	return ErrNop
 }

pkg/dbop/operator.go

@@ -54,6 +54,9 @@ type Operator interface {
 	// If `timeoutSeconds` is zero, this will not timeout.
 	WaitForGTID(ctx context.Context, gtidSet string, timeoutSeconds int) error
 
+	// SetSessionLockWaitTimeout set @@session.lock_wait_timeout to `timeoutSeconds`.
+	SetSessionLockWaitTimeout(ctx context.Context, timeoutSeconds int) error
+
 	// SetReadOnly makes the instance super_read_only if `true` is passed.
 	// Otherwise, this stops the replication and makes the instance writable.
 	SetReadOnly(context.Context, bool) error

pkg/dbop/replication.go

@@ -71,6 +71,13 @@ func (o *operator) WaitForGTID(ctx context.Context, gtid string, timeoutSeconds
 	return nil
 }
 
+func (o *operator) SetSessionLockWaitTimeout(ctx context.Context, timeoutSeconds int)  error {
+	if _, err := o.db.ExecContext(ctx, "SET SESSION lock_wait_timeout=?", timeoutSeconds); err != nil {
+		return fmt.Errorf("failed to set lock_wait_timeout: %w", err)
+	}
+	return nil
+}
+
 func (o *operator) SetReadOnly(ctx context.Context, readOnly bool) error {
 	if readOnly {
 		if _, err := o.db.ExecContext(ctx, "SET GLOBAL super_read_only=1"); err != nil {