@Override
  public boolean equals(Object other) {
    if (!(other instanceof HashIndexSet)) {
      return false;
    }
    Set that = (Set) other;
    if (that.size() != size()) {
      return false;
    }
    return containsAll(that);
  }
Locates the next available insertion index for the provided indexKey and set

@return the index of an open or resused position
geode-core/src/main/java/org/apache/geode/cache/query/internal/index/HashIndexSet.java