@Override
  public String toString() {
    StringBuilder sb = new StringBuilder();
    for (Map.Entry<String, Exception> entry : exceptionsMap.entrySet()) {
      sb.append("Creation of index: ").append(entry.getKey()).append(" failed due to: ")
          .append(entry.getValue()).append(", ");
    }
    sb.delete(sb.length() - 2, sb.length());
    return sb.toString();
  }
Returns a set of names for the indexes that failed to create

@return set of failed index names
geode-core/src/main/java/org/apache/geode/cache/query/MultiIndexCreationException.java