vschema: allow pins in vschema

data/test/vtgate/schema_test.json

@@ -156,6 +156,9 @@
             }
           ]
         },
+        "pin_test": {
+          "pinned": "80"
+        },
         "weird`name": {
           "column_vindexes": [
             {

data/test/vtgate/select_cases.txt

@@ -254,6 +254,26 @@
   }
 }
 
+# select from pinned table
+"select * from pin_test"
+{
+  "Original": "select * from pin_test",
+  "Instructions": {
+    "Opcode": "SelectEqualUnique",
+    "Keyspace": {
+      "Name": "user",
+      "Sharded": true
+    },
+    "Query": "select * from pin_test",
+    "FieldQuery": "select * from pin_test where 1 != 1",
+    "Vindex": "binary",
+    "Values": [
+      "\ufffd"
+    ]
+  }
+}
+
+
 # select from dual on sharded keyspace
 "select @@session.auto_increment_increment from user.dual"
 {

go/vt/vtgate/vindexes/vschema.go

@@ -17,6 +17,7 @@ limitations under the License.
 package vindexes
 
 import (
+	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
@@ -203,7 +204,13 @@ func buildTables(source *vschemapb.SrvVSchema, vschema *VSchema) error {
 			if table.Type == "sequence" {
 				t.IsSequence = true
 			}
-			if keyspace.Sharded && len(table.ColumnVindexes) == 0 {
+			if table.Pinned != "" {
+				decoded, err := hex.DecodeString(table.Pinned)
+				if err != nil {
+					return fmt.Errorf("could not decode the keyspace id for pin: %v", err)
+				}
+				t.Pinned = decoded
+			} else if keyspace.Sharded && len(table.ColumnVindexes) == 0 {
 				return fmt.Errorf("missing primary col vindex for table: %s", tname)
 			}
 

go/vt/vtgate/vindexes/vschema_test.go

@@ -237,6 +237,61 @@ func TestVSchemaColumnsFail(t *testing.T) {
 	}
 }
 
+func TestVSchemaPinned(t *testing.T) {
+	good := vschemapb.SrvVSchema{
+		Keyspaces: map[string]*vschemapb.Keyspace{
+			"sharded": {
+				Sharded: true,
+				Tables: map[string]*vschemapb.Table{
+					"t1": {
+						Pinned: "80",
+					},
+				},
+			},
+		},
+	}
+	got, err := BuildVSchema(&good)
+	if err != nil {
+		t.Error(err)
+	}
+	ks := &Keyspace{
+		Name:    "sharded",
+		Sharded: true,
+	}
+	t1 := &Table{
+		Name:     sqlparser.NewTableIdent("t1"),
+		Keyspace: ks,
+		Pinned:   []byte{0x80},
+	}
+	dual := &Table{
+		Name:     sqlparser.NewTableIdent("dual"),
+		Keyspace: ks,
+		Pinned:   []byte{0},
+	}
+	want := &VSchema{
+		uniqueTables: map[string]*Table{
+			"t1":   t1,
+			"dual": dual,
+		},
+		uniqueVindexes: map[string]Vindex{},
+		Keyspaces: map[string]*KeyspaceSchema{
+			"sharded": {
+				Keyspace: ks,
+				Tables: map[string]*Table{
+					"t1":   t1,
+					"dual": dual,
+				},
+				Vindexes: map[string]Vindex{},
+			},
+		},
+	}
+	if !reflect.DeepEqual(got, want) {
+		gotjson, _ := json.Marshal(got)
+		wantjson, _ := json.Marshal(want)
+		t.Errorf("BuildVSchema:\n%s, want\n%s", gotjson, wantjson)
+	}
+}
+
 func TestShardedVSchemaOwned(t *testing.T) {
 	good := vschemapb.SrvVSchema{
 		Keyspaces: map[string]*vschemapb.Keyspace{

proto/vschema.proto

@@ -60,6 +60,11 @@ message Table {
   AutoIncrement auto_increment = 3;
   // columns lists the columns for the table.
   repeated Column columns = 4;
+  // pinned pins an unsharded table to a specific
+  // shard, as dictated by the keyspace id.
+  // The keyspace id is represened in hex form
+  // like in keyranges.
+  string pinned =5;
 }
 
 // ColumnVindex is used to associate a column to a vindex.