Adds support for Show variables

go/test/endtoend/vtgate/misc_test.go

@@ -529,6 +529,23 @@ func TestFlush(t *testing.T) {
 	exec(t, conn, "flush local tables t1, t2")
 }
 
+func TestShowVariables(t *testing.T) {
+	defer cluster.PanicHandler(t)
+	ctx := context.Background()
+	conn, err := mysql.Connect(ctx, &vtParams)
+	require.NoError(t, err)
+	defer conn.Close()
+	res := exec(t, conn, "show variables like \"%version%\";")
+	found := false
+	for _, row := range res.Rows {
+		if row[0].ToString() == "version" {
+			assert.Contains(t, row[1].ToString(), "vitess")
+			found = true
+		}
+	}
+	require.True(t, found, "Expected a row for version in show query")
+}
+
 func assertMatches(t *testing.T, conn *mysql.Conn, query, expected string) {
 	t.Helper()
 	qr := exec(t, conn, query)

go/vt/sqlparser/analyzer.go

@@ -130,11 +130,17 @@ func CachePlan(stmt Statement) bool {
 	return false
 }
 
-//IsSetStatement takes Statement and returns if the statement is set statement.
-func IsSetStatement(stmt Statement) bool {
-	switch stmt.(type) {
+//MustRewriteAST takes Statement and returns true if RewriteAST must run on it for correct execution irrespective of user flags.
+func MustRewriteAST(stmt Statement) bool {
+	switch node := stmt.(type) {
 	case *Set:
 		return true
+	case *Show:
+		switch node.Internal.(type) {
+		case *ShowBasic:
+			return true
+		}
+		return false
 	}
 	return false
 }

go/vt/sqlparser/ast_rewriting.go

@@ -178,6 +178,13 @@ func (er *expressionRewriter) rewrite(cursor *Cursor) bool {
 			node.Expr = aliasTableName
 			cursor.Replace(node)
 		}
+	case *ShowBasic:
+		if node.Command == VariableGlobal || node.Command == VariableSession {
+			varsToAdd := sysvars.GetInterestingVariables()
+			for _, sysVar := range varsToAdd {
+				er.bindVars.AddSysVar(sysVar)
+			}
+		}
 	}
 	return true
 }

go/vt/sqlparser/ast_rewriting_test.go

@@ -181,6 +181,40 @@ func TestRewrites(in *testing.T) {
 		in:       "CALL proc(@foo)",
 		expected: "CALL proc(:__vtudvfoo)",
 		udv:      1,
+	}, {
+		in:                          "SHOW VARIABLES",
+		expected:                    "SHOW VARIABLES",
+		autocommit:                  true,
+		clientFoundRows:             true,
+		skipQueryPlanCache:          true,
+		sqlSelectLimit:              true,
+		transactionMode:             true,
+		workload:                    true,
+		version:                     true,
+		versionComment:              true,
+		ddlStrategy:                 true,
+		sessionUUID:                 true,
+		sessionEnableSystemSettings: true,
+		rawGTID:                     true,
+		rawTimeout:                  true,
+		sessTrackGTID:               true,
+	}, {
+		in:                          "SHOW GLOBAL VARIABLES",
+		expected:                    "SHOW GLOBAL VARIABLES",
+		autocommit:                  true,
+		clientFoundRows:             true,
+		skipQueryPlanCache:          true,
+		sqlSelectLimit:              true,
+		transactionMode:             true,
+		workload:                    true,
+		version:                     true,
+		versionComment:              true,
+		ddlStrategy:                 true,
+		sessionUUID:                 true,
+		sessionEnableSystemSettings: true,
+		rawGTID:                     true,
+		rawTimeout:                  true,
+		sessTrackGTID:               true,
 	}}
 
 	for _, tc := range tests {

go/vt/sysvars/sysvars.go

@@ -238,3 +238,16 @@ var (
 		{Name: "version_tokens_session"},
 	}
 )
+
+// GetInterestingVariables is used to return all the variables that may be listed in a SHOW VARIABLES command.
+func GetInterestingVariables() []string {
+	var res []string
+	// Add all the vitess aware variables
+	for _, variable := range VitessAware {
+		res = append(res, variable.Name)
+	}
+	// Also add version and version comment
+	res = append(res, Version.Name)
+	res = append(res, VersionComment.Name)
+	return res
+}

go/vt/vtgate/engine/replace_variables.go

@@ -0,0 +1,97 @@
+/*
+Copyright 2021 The Vitess Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package engine
+
+import (
+	"vitess.io/vitess/go/sqltypes"
+	querypb "vitess.io/vitess/go/vt/proto/query"
+)
+
+var _ Primitive = (*ReplaceVariables)(nil)
+
+// ReplaceVariables is used in SHOW VARIABLES statements so that it replaces the values for vitess-aware variables
+type ReplaceVariables struct {
+	Input Primitive
+	noTxNeeded
+}
+
+// NewReplaceVariables is used to create a new ReplaceVariables primitive
+func NewReplaceVariables(input Primitive) *ReplaceVariables {
+	return &ReplaceVariables{Input: input}
+}
+
+// RouteType implements the Primitive interface
+func (r *ReplaceVariables) RouteType() string {
+	return r.Input.RouteType()
+}
+
+// GetKeyspaceName implements the Primitive interface
+func (r *ReplaceVariables) GetKeyspaceName() string {
+	return r.Input.GetKeyspaceName()
+}
+
+// GetTableName implements the Primitive interface
+func (r *ReplaceVariables) GetTableName() string {
+	return r.Input.GetTableName()
+}
+
+// Execute implements the Primitive interface
+func (r *ReplaceVariables) Execute(vcursor VCursor, bindVars map[string]*querypb.BindVariable, wantfields bool) (*sqltypes.Result, error) {
+	qr, err := r.Input.Execute(vcursor, bindVars, wantfields)
+	if err != nil {
+		return nil, err
+	}
+	replaceVariables(qr, bindVars)
+	return qr, nil
+}
+
+// StreamExecute implements the Primitive interface
+func (r *ReplaceVariables) StreamExecute(vcursor VCursor, bindVars map[string]*querypb.BindVariable, wantfields bool, callback func(*sqltypes.Result) error) error {
+	innerCallback := callback
+	callback = func(result *sqltypes.Result) error {
+		replaceVariables(result, bindVars)
+		return innerCallback(result)
+	}
+	return r.Input.StreamExecute(vcursor, bindVars, wantfields, callback)
+}
+
+// GetFields implements the Primitive interface
+func (r *ReplaceVariables) GetFields(vcursor VCursor, bindVars map[string]*querypb.BindVariable) (*sqltypes.Result, error) {
+	return r.Input.GetFields(vcursor, bindVars)
+}
+
+// Inputs implements the Primitive interface
+func (r *ReplaceVariables) Inputs() []Primitive {
+	return []Primitive{r.Input}
+}
+
+// description implements the Primitive interface
+func (r *ReplaceVariables) description() PrimitiveDescription {
+	return PrimitiveDescription{
+		OperatorType: "ReplaceVariables",
+	}
+}
+
+func replaceVariables(qr *sqltypes.Result, bindVars map[string]*querypb.BindVariable) {
+	for i, row := range qr.Rows {
+		variableName := row[0].ToString()
+		res, found := bindVars["__vt"+variableName]
+		if found {
+			qr.Rows[i][1] = sqltypes.NewVarChar(string(res.GetValue()))
+		}
+	}
+}

go/vt/vtgate/executor.go

@@ -1237,7 +1237,7 @@ func (e *Executor) getPlan(vcursor *vcursorImpl, sql string, comments sqlparser.
 	vcursor.SetIgnoreMaxMemoryRows(ignoreMaxMemoryRows)
 
 	// Normalize if possible and retry.
-	if (e.normalize && sqlparser.CanNormalize(stmt)) || sqlparser.IsSetStatement(stmt) {
+	if (e.normalize && sqlparser.CanNormalize(stmt)) || sqlparser.MustRewriteAST(stmt) {
 		parameterize := e.normalize // the public flag is called normalize
 		result, err := sqlparser.PrepareAST(stmt, bindVars, "vtg", parameterize, vcursor.keyspace)
 		if err != nil {

go/vt/vtgate/planbuilder/show.go

@@ -54,9 +54,10 @@ func buildShowBasicPlan(show *sqlparser.ShowBasic, vschema ContextVSchema) (engi
 	switch show.Command {
 	case sqlparser.Charset:
 		return buildCharsetPlan(show)
-	case sqlparser.Collation, sqlparser.Function, sqlparser.Privilege, sqlparser.Procedure,
-		sqlparser.VariableGlobal, sqlparser.VariableSession:
+	case sqlparser.Collation, sqlparser.Function, sqlparser.Privilege, sqlparser.Procedure:
 		return buildSendAnywherePlan(show, vschema)
+	case sqlparser.VariableGlobal, sqlparser.VariableSession:
+		return buildVariablePlan(show, vschema)
 	case sqlparser.Column, sqlparser.Index:
 		return buildShowTblPlan(show, vschema)
 	case sqlparser.Database, sqlparser.Keyspace:
@@ -98,6 +99,15 @@ func buildSendAnywherePlan(show *sqlparser.ShowBasic, vschema ContextVSchema) (e
 	}, nil
 }
 
+func buildVariablePlan(show *sqlparser.ShowBasic, vschema ContextVSchema) (engine.Primitive, error) {
+	plan, err := buildSendAnywherePlan(show, vschema)
+	if err != nil {
+		return nil, err
+	}
+	plan = engine.NewReplaceVariables(plan)
+	return plan, nil
+}
+
 func buildShowTblPlan(show *sqlparser.ShowBasic, vschema ContextVSchema) (engine.Primitive, error) {
 	if show.DbName != "" {
 		show.Tbl.Qualifier = sqlparser.NewTableIdent(show.DbName)

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

@@ -220,15 +220,43 @@
   "QueryType": "SHOW",
   "Original": "show variables",
   "Instructions": {
-    "OperatorType": "Send",
-    "Keyspace": {
-      "Name": "main",
-      "Sharded": false
-    },
-    "TargetDestination": "AnyShard()",
-    "IsDML": false,
-    "Query": "show variables",
-    "SingleShardOnly": true
+    "OperatorType": "ReplaceVariables",
+    "Inputs": [
+      {
+        "OperatorType": "Send",
+        "Keyspace": {
+          "Name": "main",
+          "Sharded": false
+        },
+        "TargetDestination": "AnyShard()",
+        "IsDML": false,
+        "Query": "show variables",
+        "SingleShardOnly": true
+      }
+    ]
+  }
+}
+
+# show global variables
+"show global variables"
+{
+  "QueryType": "SHOW",
+  "Original": "show global variables",
+  "Instructions": {
+    "OperatorType": "ReplaceVariables",
+    "Inputs": [
+      {
+        "OperatorType": "Send",
+        "Keyspace": {
+          "Name": "main",
+          "Sharded": false
+        },
+        "TargetDestination": "AnyShard()",
+        "IsDML": false,
+        "Query": "show global variables",
+        "SingleShardOnly": true
+      }
+    ]
   }
 }
 

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

@@ -40,14 +40,19 @@
   "QueryType": "SHOW",
   "Original": "show variables",
   "Instructions": {
-    "OperatorType": "Send",
-    "Keyspace": {
-      "Name": "main",
-      "Sharded": false
-    },
-    "TargetDestination": "AnyShard()",
-    "IsDML": false,
-    "Query": "show variables",
-    "SingleShardOnly": true
+    "OperatorType": "ReplaceVariables",
+    "Inputs": [
+      {
+        "OperatorType": "Send",
+        "Keyspace": {
+          "Name": "main",
+          "Sharded": false
+        },
+        "TargetDestination": "AnyShard()",
+        "IsDML": false,
+        "Query": "show variables",
+        "SingleShardOnly": true
+      }
+    ]
   }
 }