mcp: use QueryExecModeExec for redshift access (#68250)

lib/client/db/postgres/mcp/mcp.go

@@ -28,6 +28,7 @@ import (
 	"github.com/jackc/pgx/v5/pgxpool"
 	"github.com/mark3labs/mcp-go/mcp"
 
+	"github.com/gravitational/teleport/api/types"
 	dbmcp "github.com/gravitational/teleport/lib/client/db/mcp"
 	clientmcp "github.com/gravitational/teleport/lib/client/mcp"
 	"github.com/gravitational/teleport/lib/defaults"
@@ -256,14 +257,28 @@ func buildConnConfig(db *dbmcp.Database) (*pgxpool.Config, error) {
 		applicationNameParamName: applicationNameParamValue,
 	}
 	config.ConnConfig.TLSConfig = nil
-	// Use simple protocol to have a closer behavior to DB REPL and psql.
-	//
-	// This also avoids each query being prepared, binded and executed, reducing
-	// the amount of audit events per query executed.
-	config.ConnConfig.DefaultQueryExecMode = pgx.QueryExecModeSimpleProtocol
+	config.ConnConfig.DefaultQueryExecMode = queryExecModeForDatabase(db.DB)
 	return config, nil
 }
 
+func queryExecModeForDatabase(db types.Database) pgx.QueryExecMode {
+	switch db.GetType() {
+	case types.DatabaseTypeRedshift, types.DatabaseTypeRedshiftServerless:
+		// Redshift does not report standard_conforming_strings in the same way
+		// PostgreSQL does, which makes pgx reject simple protocol queries before
+		// sending them. QueryExecModeExec uses the extended query protocol without
+		// pgx statement caching, so it avoids the simple protocol sanitizer while
+		// staying suitable for ad-hoc SQL generated through MCP.
+		return pgx.QueryExecModeExec
+	default:
+		// Use simple protocol to have a closer behavior to DB REPL and psql.
+		//
+		// This also avoids each query being prepared, bound, and executed, reducing
+		// the amount of audit events per query executed.
+		return pgx.QueryExecModeSimpleProtocol
+	}
+}
+
 const (
 	// queryToolDatabaseParam is the name of the database URI param name from
 	// query tool.

lib/client/db/postgres/mcp/mcp_test.go

@@ -62,6 +62,48 @@ func TestFormatResult(t *testing.T) {
 	}
 }
 
+func TestQueryExecModeForDatabase(t *testing.T) {
+	for name, tc := range map[string]struct {
+		spec databaseSpec
+		want pgx.QueryExecMode
+	}{
+		"postgres uses simple protocol": {
+			spec: databaseSpec{
+				protocol: defaults.ProtocolPostgres,
+			},
+			want: pgx.QueryExecModeSimpleProtocol,
+		},
+		"redshift uses exec mode": {
+			spec: databaseSpec{
+				protocol: defaults.ProtocolPostgres,
+				aws: types.AWS{
+					Region:   "us-east-1",
+					Redshift: types.Redshift{ClusterID: "redshift-cluster"},
+				},
+			},
+			want: pgx.QueryExecModeExec,
+		},
+		"redshift serverless uses exec mode": {
+			spec: databaseSpec{
+				protocol: defaults.ProtocolPostgres,
+				aws: types.AWS{
+					Region: "us-east-1",
+					RedshiftServerless: types.RedshiftServerless{
+						WorkgroupName: "redshift-workgroup",
+					},
+				},
+			},
+			want: pgx.QueryExecModeExec,
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			db, err := newTestDatabase(tc.spec)
+			require.NoError(t, err)
+			require.Equal(t, tc.want, queryExecModeForDatabase(db))
+		})
+	}
+}
+
 func TestFormatErrors(t *testing.T) {
 	// Dummy listener that always drop connections.
 	listener := listener.NewInMemoryListener()
@@ -177,6 +219,21 @@ func TestFormatErrors(t *testing.T) {
 	}
 }
 
+type databaseSpec struct {
+	protocol string
+	aws      types.AWS
+}
+
+func newTestDatabase(spec databaseSpec) (types.Database, error) {
+	return types.NewDatabaseV3(types.Metadata{
+		Name: "test-db",
+	}, types.DatabaseSpecV3{
+		Protocol: spec.protocol,
+		URI:      "localhost:5432",
+		AWS:      spec.aws,
+	})
+}
+
 func newMockRows(commandTag string, fields []string, rows [][]any) pgx.Rows {
 	var fds []pgconn.FieldDescription
 	for _, fieldName := range fields {