passthrough system settings disabled by default

go/test/endtoend/cluster/vtgate_process.go

@@ -53,6 +53,7 @@ type VtgateProcess struct {
 	MySQLAuthServerImpl   string
 	Directory             string
 	VerifyURL             string
+	SysVarSetEnabled      bool
 	//Extra Args to be set before starting the vtgate process
 	ExtraArgs []string
 
@@ -63,8 +64,7 @@ type VtgateProcess struct {
 // Setup starts Vtgate process with required arguements
 func (vtgate *VtgateProcess) Setup() (err error) {
 
-	vtgate.proc = exec.Command(
-		vtgate.Binary,
+	args := []string{
 		"-topo_implementation", vtgate.CommonArg.TopoImplementation,
 		"-topo_global_server_address", vtgate.CommonArg.TopoGlobalAddress,
 		"-topo_global_root", vtgate.CommonArg.TopoGlobalRoot,
@@ -80,6 +80,13 @@ func (vtgate *VtgateProcess) Setup() (err error) {
 		"-gateway_implementation", vtgate.GatewayImplementation,
 		"-service_map", vtgate.ServiceMap,
 		"-mysql_auth_server_impl", vtgate.MySQLAuthServerImpl,
+	}
+	if vtgate.SysVarSetEnabled {
+		args = append(args, "-enable_system_settings")
+	}
+	vtgate.proc = exec.Command(
+		vtgate.Binary,
+		args...,
 	)
 	if *isCoverage {
 		vtgate.proc.Args = append(vtgate.proc.Args, "-test.coverprofile="+getCoveragePath("vtgate.out"))

go/test/endtoend/vtgate/setstatement/main_test.go

@@ -120,7 +120,9 @@ func TestMain(m *testing.M) {
 		}
 
 		// Start vtgate
-		if err := clusterInstance.StartVtgate(); err != nil {
+		vtgateProcess := clusterInstance.NewVtgateInstance()
+		vtgateProcess.SysVarSetEnabled = true
+		if err := vtgateProcess.Setup(); err != nil {
 			return 1
 		}
 

go/vt/vtgate/executor_set_test.go

@@ -268,6 +268,7 @@ func TestExecutorSet(t *testing.T) {
 
 func TestExecutorSetOp(t *testing.T) {
 	executor, _, _, sbclookup := createLegacyExecutorEnv()
+	*sysVarSetEnabled = true
 
 	sbclookup.SetResults([]*sqltypes.Result{
 		sqltypes.MakeTestResult(sqltypes.MakeTestFields("sql_mode", "varchar"), "STRICT_ALL_TABLES,NO_AUTO_UPDATES"),

go/vt/vtgate/planbuilder/builder.go

@@ -132,6 +132,7 @@ type ContextVSchema interface {
 	TargetDestination(qualifier string) (key.Destination, *vindexes.Keyspace, topodatapb.TabletType, error)
 	AnyKeyspace() (*vindexes.Keyspace, error)
 	FirstSortedKeyspace() (*vindexes.Keyspace, error)
+	SysVarSetEnabled() bool
 }
 
 //-------------------------------------------------------------------------

go/vt/vtgate/planbuilder/plan_test.go

@@ -147,7 +147,8 @@ func init() {
 
 func TestPlan(t *testing.T) {
 	vschemaWrapper := &vschemaWrapper{
-		v: loadSchema(t, "schema_test.json"),
+		v:             loadSchema(t, "schema_test.json"),
+		sysVarEnabled: true,
 	}
 
 	testOutputTempDir, err := ioutil.TempDir("", "plan_test")
@@ -178,6 +179,18 @@ func TestPlan(t *testing.T) {
 	testFile(t, "lock_cases.txt", testOutputTempDir, vschemaWrapper)
 }
 
+func TestSysVarSetDisabled(t *testing.T) {
+	vschemaWrapper := &vschemaWrapper{
+		v:             loadSchema(t, "schema_test.json"),
+		sysVarEnabled: false,
+	}
+
+	testOutputTempDir, err := ioutil.TempDir("", "plan_test")
+	require.NoError(t, err)
+	defer os.RemoveAll(testOutputTempDir)
+	testFile(t, "set_sysvar_disabled_cases.txt", testOutputTempDir, vschemaWrapper)
+}
+
 func TestOne(t *testing.T) {
 	vschema := &vschemaWrapper{
 		v: loadSchema(t, "schema_test.json"),
@@ -258,10 +271,15 @@ func loadSchema(t *testing.T, filename string) *vindexes.VSchema {
 var _ ContextVSchema = (*vschemaWrapper)(nil)
 
 type vschemaWrapper struct {
-	v          *vindexes.VSchema
-	keyspace   *vindexes.Keyspace
-	tabletType topodatapb.TabletType
-	dest       key.Destination
+	v             *vindexes.VSchema
+	keyspace      *vindexes.Keyspace
+	tabletType    topodatapb.TabletType
+	dest          key.Destination
+	sysVarEnabled bool
+}
+
+func (vw *vschemaWrapper) SysVarSetEnabled() bool {
+	return vw.sysVarEnabled
 }
 
 func (vw *vschemaWrapper) TargetDestination(qualifier string) (key.Destination, *vindexes.Keyspace, topodatapb.TabletType, error) {

go/vt/vtgate/planbuilder/set.go

@@ -351,6 +351,9 @@ func expressionOkToDelegateToTablet(e sqlparser.Expr) bool {
 }
 
 func buildSetOpVarSet(expr *sqlparser.SetExpr, vschema ContextVSchema) (engine.SetOp, error) {
+	if !vschema.SysVarSetEnabled() {
+		return buildSetOpCheckAndIgnore(expr, vschema)
+	}
 	ks, err := vschema.AnyKeyspace()
 	if err != nil {
 		return nil, err

go/vt/vtgate/planbuilder/testdata/set_sysvar_disabled_cases.txt

@@ -0,0 +1,36 @@
+# set passthrough disabled - check and ignore plan
+"set @@sql_mode = concat(@@sql_mode, ',NO_AUTO_CREATE_USER'), @@sql_safe_updates = 1"
+{
+  "QueryType": "SET",
+  "Original": "set @@sql_mode = concat(@@sql_mode, ',NO_AUTO_CREATE_USER'), @@sql_safe_updates = 1",
+  "Instructions": {
+    "OperatorType": "Set",
+    "Ops": [
+      {
+        "Type": "SysVarCheckAndIgnore",
+        "Name": "sql_mode",
+        "Keyspace": {
+          "Name": "main",
+          "Sharded": false
+        },
+        "TargetDestination": {},
+        "Expr": "concat(@@sql_mode, ',NO_AUTO_CREATE_USER')"
+      },
+      {
+        "Type": "SysVarCheckAndIgnore",
+        "Name": "sql_safe_updates",
+        "Keyspace": {
+          "Name": "main",
+          "Sharded": false
+        },
+        "TargetDestination": {},
+        "Expr": "1"
+      }
+    ],
+    "Inputs": [
+      {
+        "OperatorType": "SingleRow"
+      }
+    ]
+  }
+}

go/vt/vtgate/vcursor_impl.go

@@ -467,6 +467,10 @@ func (vc *vcursorImpl) TargetDestination(qualifier string) (key.Destination, *vi
 	return vc.destination, keyspace.Keyspace, vc.tabletType, nil
 }
 
+func (vc *vcursorImpl) SysVarSetEnabled() bool {
+	return *sysVarSetEnabled
+}
+
 // ParseDestinationTarget parses destination target string and sets default keyspace if possible.
 func parseDestinationTarget(targetString string, vschema *vindexes.VSchema) (string, topodatapb.TabletType, key.Destination, error) {
 	destKeyspace, destTabletType, dest, err := topoprotopb.ParseDestination(targetString, defaultTabletType)

go/vt/vtgate/vtgate.go

@@ -69,6 +69,9 @@ var (
 	HealthCheckTimeout = flag.Duration("healthcheck_timeout", time.Minute, "the health check timeout period")
 	maxPayloadSize     = flag.Int("max_payload_size", 0, "The threshold for query payloads in bytes. A payload greater than this threshold will result in a failure to handle the query.")
 	warnPayloadSize    = flag.Int("warn_payload_size", 0, "The warning threshold for query payloads in bytes. A payload greater than this threshold will cause the VtGateWarnings.WarnPayloadSizeExceeded counter to be incremented.")
+
+	// Put set-passthrough under a flag.
+	sysVarSetEnabled = flag.Bool("enable_system_settings", false, "This will enable the system settings to be changed per session at the database connection level")
 )
 
 func getTxMode() vtgatepb.TransactionMode {