Add support for transaction access mode (vitessio#11704)

* feat: added transaction access mode to proto

Signed-off-by: Harshit Gangal <[email protected]>

* refactor: tx_pool create transaction code

Signed-off-by: Harshit Gangal <[email protected]>

* feat: use tx access mode in vttablet and set that when starting a transaction

Signed-off-by: Harshit Gangal <[email protected]>

* feat: reset transaction access mode after commit/rollback/release

Signed-off-by: Harshit Gangal <[email protected]>

* feat: added parsing support for start transaction with characteristics

Signed-off-by: Harshit Gangal <[email protected]>

* feat: set the transaction characteristics in execute option on start transaction statement

Signed-off-by: Harshit Gangal <[email protected]>

* refactor: little tx_pool refactor

Signed-off-by: Harshit Gangal <[email protected]>

* test: added e2e test for tx access modes

Signed-off-by: Harshit Gangal <[email protected]>

* added release notes

Signed-off-by: Harshit Gangal <[email protected]>

* addressed review comments

Signed-off-by: Harshit Gangal <[email protected]>

* generated protobuf files updated

Signed-off-by: Harshit Gangal <[email protected]>

Signed-off-by: Harshit Gangal <[email protected]>

doc/releasenotes/16_0_0_summary.md

@@ -92,3 +92,37 @@ is now fixed. The full issue can be found [here](https://github.com/vitessio/vit
 ### Deprecations
 
 The V3 planner is deprecated as of the V16 release, and will be removed in the V17 release of Vitess.
+
+### MySQL Compatibility
+
+#### Transaction Isolation Level
+Support added for `set [session] transaction isolation level <transaction_characteristic>`
+```sql
+transaction_characteristic: {
+    ISOLATION LEVEL level
+  | access_mode
+}
+
+level: {
+     REPEATABLE READ
+   | READ COMMITTED
+   | READ UNCOMMITTED
+   | SERIALIZABLE
+}
+```
+This will set the transaction isolation level for the current session. 
+This will be applied to any shard where the session will open a transaction.
+
+#### Transaction Access Mode
+Support added for `start transaction` with transaction characteristic.
+```sql
+START TRANSACTION
+    [transaction_characteristic [, transaction_characteristic] ...]
+
+transaction_characteristic: {
+    WITH CONSISTENT SNAPSHOT
+  | READ WRITE
+  | READ ONLY
+}
+```
+This will allow users to start a transaction with these characteristics.

go/test/endtoend/vtgate/transaction/trxn_test.go → go/test/endtoend/vtgate/transaction/tx_test.go

@@ -174,3 +174,56 @@ func TestTransactionIsolation(t *testing.T) {
 	utils.AssertMatches(t, conn1, "select id, msg from test where id = 1", `[[INT64(1) VARCHAR("foo")]]`)
 	utils.Exec(t, conn1, "rollback")
 }
+
+func TestTransactionAccessModes(t *testing.T) {
+	closer := start(t)
+	defer closer()
+
+	ctx := context.Background()
+
+	conn, err := mysql.Connect(ctx, &vtParams)
+	require.NoError(t, err)
+	defer conn.Close()
+
+	// start a transaction with read-only characteristic.
+	utils.Exec(t, conn, "start transaction read only")
+	_, err = utils.ExecAllowError(t, conn, "insert into test(id, msg) values (42,'foo')")
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "Cannot execute statement in a READ ONLY transaction")
+	utils.Exec(t, conn, "rollback")
+
+	// trying autocommit, this should pass as transaction characteristics are limited to single transaction.
+	utils.Exec(t, conn, "insert into test(id, msg) values (42,'foo')")
+
+	// target replica
+	utils.Exec(t, conn, "use `ks@replica`")
+	// start a transaction with read-only characteristic.
+	utils.Exec(t, conn, "start transaction read only")
+	utils.Exec(t, conn, "select * from test")
+
+	// start a transaction with read-write characteristic. This should fail
+	utils.Exec(t, conn, "start transaction read write")
+	_, err = utils.ExecAllowError(t, conn, "select connection_id()")
+	require.Error(t, err)
+	require.Contains(t, err.Error(), "cannot start read write transaction on a read only tablet")
+	utils.Exec(t, conn, "rollback")
+}
+
+func start(t *testing.T) func() {
+	deleteAll := func() {
+		conn, err := mysql.Connect(context.Background(), &vtParams)
+		require.NoError(t, err)
+		tables := []string{"test", "twopc_user"}
+		for _, table := range tables {
+			_, _ = utils.ExecAllowError(t, conn, "delete from "+table)
+		}
+		conn.Close()
+	}
+
+	deleteAll()
+
+	return func() {
+		deleteAll()
+		cluster.PanicHandler(t)
+	}
+}

go/vt/sqlparser/ast.go

@@ -562,8 +562,13 @@ type (
 		DBName IdentifierCS
 	}
 
+	// TxAccessMode is an enum for Transaction Access Mode
+	TxAccessMode int8
+
 	// Begin represents a Begin statement.
-	Begin struct{}
+	Begin struct {
+		TxAccessModes []TxAccessMode
+	}
 
 	// Commit represents a Commit statement.
 	Commit struct{}

go/vt/sqlparser/ast_format.go

@@ -963,7 +963,19 @@ func (node *Commit) Format(buf *TrackedBuffer) {
 
 // Format formats the node.
 func (node *Begin) Format(buf *TrackedBuffer) {
-	buf.literal("begin")
+	if node.TxAccessModes == nil {
+		buf.literal("begin")
+		return
+	}
+	buf.literal("start transaction")
+	for idx, accessMode := range node.TxAccessModes {
+		if idx == 0 {
+			buf.astPrintf(node, " %s", accessMode.ToString())
+			continue
+		}
+		buf.astPrintf(node, ", %s", accessMode.ToString())
+	}
+
 }
 
 // Format formats the node.

go/vt/sqlparser/ast_funcs.go

@@ -1895,6 +1895,20 @@ func (columnFormat ColumnFormat) ToString() string {
 	}
 }
 
+// ToString returns the TxAccessMode type as a string
+func (ty TxAccessMode) ToString() string {
+	switch ty {
+	case WithConsistentSnapshot:
+		return WithConsistentSnapshotStr
+	case ReadWrite:
+		return ReadWriteStr
+	case ReadOnly:
+		return ReadOnlyStr
+	default:
+		return "Unknown Transaction Access Mode"
+	}
+}
+
 // CompliantName is used to get the name of the bind variable to use for this column name
 func (node *ColName) CompliantName() string {
 	if !node.Qualifier.IsEmpty() {

go/vt/sqlparser/constants.go

@@ -238,6 +238,11 @@ const (
 	RepeatableReadStr  = "repeatable-read"
 	SerializableStr    = "serializable"
 
+	// Transaction access mode
+	WithConsistentSnapshotStr = "with consistent snapshot"
+	ReadWriteStr              = "read write"
+	ReadOnlyStr               = "read only"
+
 	// Explain formats
 	EmptyStr       = ""
 	TreeStr        = "tree"
@@ -859,3 +864,10 @@ const (
 	IntervalMinuteMicrosecond
 	IntervalSecondMicrosecond
 )
+
+// Transaction access mode
+const (
+	WithConsistentSnapshot TxAccessMode = iota
+	ReadWrite
+	ReadOnly
+)