[release-20.0] VTGate MoveTables Buffering: Fix panic when buffering …

…is disabled (#16922) (#16935)

Signed-off-by: Rohit Nayak <[email protected]>
Signed-off-by: Harshit Gangal <[email protected]>
Co-authored-by: vitess-bot[bot] <108069721+vitess-bot[bot]@users.noreply.github.com>
Co-authored-by: Harshit Gangal <[email protected]>

go/vt/vtgate/executor_test.go

@@ -1511,6 +1511,20 @@ func TestExecutorUnrecognized(t *testing.T) {
 	require.Error(t, err, "unrecognized statement: invalid statement'")
 }
 
+func TestExecutorDeniedErrorNoBuffer(t *testing.T) {
+	executor, sbc1, _, _, ctx := createExecutorEnv(t)
+	sbc1.EphemeralShardErr = errors.New("enforce denied tables")
+
+	vschemaWaitTimeout = 500 * time.Millisecond
+
+	session := NewAutocommitSession(&vtgatepb.Session{TargetString: "@primary"})
+	startExec := time.Now()
+	_, err := executor.Execute(ctx, nil, "TestExecutorDeniedErrorNoBuffer", session, "select * from user", nil)
+	require.NoError(t, err, "enforce denied tables not buffered")
+	endExec := time.Now()
+	require.GreaterOrEqual(t, endExec.Sub(startExec).Milliseconds(), int64(500))
+}
+
 // TestVSchemaStats makes sure the building and displaying of the
 // VSchemaStats works.
 func TestVSchemaStats(t *testing.T) {

go/vt/vtgate/plan_execute.go

@@ -37,6 +37,8 @@ import (
 type planExec func(ctx context.Context, plan *engine.Plan, vc *vcursorImpl, bindVars map[string]*querypb.BindVariable, startTime time.Time) error
 type txResult func(sqlparser.StatementType, *sqltypes.Result) error
 
+var vschemaWaitTimeout = 30 * time.Second
+
 func waitForNewerVSchema(ctx context.Context, e *Executor, lastVSchemaCreated time.Time, timeout time.Duration) bool {
 	pollingInterval := 10 * time.Millisecond
 	waitCtx, cancel := context.WithTimeout(ctx, timeout)
@@ -104,7 +106,10 @@ func (e *Executor) newExecute(
 			// based on the buffering configuration. This way we should be able to perform the max retries
 			// within the given window of time for most queries and we should not end up waiting too long
 			// after the traffic switch fails or the buffer window has ended, retrying old queries.
-			timeout := e.resolver.scatterConn.gateway.buffer.GetConfig().MaxFailoverDuration / (MaxBufferingRetries - 1)
+			timeout := vschemaWaitTimeout
+			if e.resolver.scatterConn.gateway.buffer != nil && e.resolver.scatterConn.gateway.buffer.GetConfig() != nil {
+				timeout = e.resolver.scatterConn.gateway.buffer.GetConfig().MaxFailoverDuration / (MaxBufferingRetries - 1)
+			}
 			if waitForNewerVSchema(ctx, e, lastVSchemaCreated, timeout) {
 				vs = e.VSchema()
 				lastVSchemaCreated = vs.GetCreated()