feat: rebuild global tables after schema has augmented the vschema

Signed-off-by: Manan Gupta <manan@planetscale.com>

go/vt/vtgate/vindexes/vschema.go

@@ -331,9 +331,9 @@ func BuildVSchema(source *vschemapb.SrvVSchema, parser *sqlparser.Parser) (vsche
 		created:        time.Now(),
 	}
 	buildKeyspaces(source, vschema, parser)
-	// buildGlobalTables before buildReferences so that buildReferences can
+	// BuildGlobalTables before buildReferences so that buildReferences can
 	// resolve sources which reference global tables.
-	buildGlobalTables(source, vschema)
+	BuildGlobalTables(source, vschema)
 	buildReferences(source, vschema)
 	buildRoutingRule(source, vschema, parser)
 	buildShardRoutingRule(source, vschema)
@@ -437,7 +437,12 @@ func (vschema *VSchema) AddUDF(ksname, udfName string) error {
 	return nil
 }
 
-func buildGlobalTables(source *vschemapb.SrvVSchema, vschema *VSchema) {
+// BuildGlobalTables rebuilds the global tables map that is used for global routing.
+// If a table name is unique across all keyspaces, then Vitess allows the users to use the table
+// without needing to select a database first.
+func BuildGlobalTables(source *vschemapb.SrvVSchema, vschema *VSchema) {
+	// Reinitialize the global Tables map to restart the building process.
+	vschema.globalTables = make(map[string]*Table)
 	for ksname, ks := range source.Keyspaces {
 		ksvschema := vschema.Keyspaces[ksname]
 		// If the keyspace requires explicit routing, don't include any of

go/vt/vtgate/vschema_manager.go

@@ -196,6 +196,8 @@ func (vm *VSchemaManager) buildAndEnhanceVSchema(v *vschemapb.SrvVSchema) *vinde
 		// We mark the keyspaces that have foreign key management in Vitess and have cyclic foreign keys
 		// to have an error. This makes all queries against them to fail.
 		markErrorIfCyclesInFk(vschema)
+		// We build the global routing table again because schema tracking might have added more tables to the vschema.
+		vindexes.BuildGlobalTables(v, vschema)
 	}
 	return vschema
 }