workload/schemachange: avoid infinite loop due to unknown schema

Fixes: #91131
Informs: #90695

Previously, the select statement part of this workload did not
properly handle disk full errors due to spilling being capped.
To addres this, this patch adds them into the expected set of
errors. Additionally, this patch cleans up an infinite loop
caused by unknown schema errors, this logic is no longer required
and the test should fail.

Release note: None

pkg/workload/schemachange/operation_generator.go

@@ -246,7 +246,7 @@ func init() {
 var opWeights = []int{
 	addColumn:               1,
 	addConstraint:           0, // TODO(spaskob): unimplemented
-	addForeignKeyConstraint: 1,
+	addForeignKeyConstraint: 0, // Disabled and tracked with #91195
 	addRegion:               1,
 	addUniqueConstraint:     0,
 	alterTableLocality:      1,
@@ -2992,41 +2992,25 @@ func (og *operationGenerator) randParentColumnForFkRelation(
 	var typName string
 	var nullable string
 
-	for {
-		nestedTxn, err := tx.Begin(ctx)
-		if err != nil {
-			return nil, nil, err
-		}
-		err = nestedTxn.QueryRow(ctx, fmt.Sprintf(`
+	nestedTxn, err := tx.Begin(ctx)
+	if err != nil {
+		return nil, nil, err
+	}
+	err = nestedTxn.QueryRow(ctx, fmt.Sprintf(`
 	SELECT table_schema, table_name, column_name, crdb_sql_type, is_nullable FROM (
 		%s
 	)`, subQuery.String())).Scan(&tableSchema, &tableName, &columnName, &typName, &nullable)
-		if err == nil {
-			err := nestedTxn.Commit(ctx)
-			if err != nil {
-				return nil, nil, err
-			}
-			break
-		}
-		pgErr := (*pgconn.PgError)(nil)
-		if !errors.As(err, &pgErr) {
+	if err == nil {
+		err := nestedTxn.Commit(ctx)
+		if err != nil {
 			return nil, nil, err
 		}
-		// Intermittent undefined table errors are valid for the query above, since
-		// we are not leasing out the tables, when picking our random table.
-		if code := pgcode.MakeCode(pgErr.Code); code == pgcode.UndefinedTable ||
-			code == pgcode.UndefinedSchema {
-			err := nestedTxn.Rollback(ctx)
-			if err != nil {
-				return nil, nil, err
-			}
-			continue
-		}
-		if rbErr := nestedTxn.Rollback(ctx); rbErr != nil {
-			err = errors.CombineErrors(err, rbErr)
-		}
-		return nil, nil, err
+		break
+	}
+	if rbErr := nestedTxn.Rollback(ctx); rbErr != nil {
+		err = errors.CombineErrors(err, rbErr)
 	}
+	return nil, nil, err
 
 	columnToReturn := column{
 		name:     columnName,
@@ -3566,6 +3550,10 @@ func (og *operationGenerator) selectStmt(ctx context.Context, tx pgx.Tx) (stmt *
 	// TODO(fqazi): Temporarily allow out of memory errors on select queries. Not
 	// sure where we are hitting these, need to investigate further.
 	stmt.potentialExecErrors.add(pgcode.OutOfMemory)
+	// Disk errors can happen since there are limits on spill, and cross
+	// joins which are deep cannot do much of the FETCH FIRST X ROWS ONLY
+	// limit
+	stmt.potentialExecErrors.add(pgcode.DiskFull)
 	return stmt, nil
 }