@Override
  public Set keySet(boolean allowTombstones) {
    checkReadiness();
    return Collections.unmodifiableSet(new KeysSet(allowTombstones));
  }
This method returns set of all the keys of this PartitionedRegion(locally or remotely).

@return set of all the keys of this PartitionedRegion

        OVERRIDES
geode-core/src/main/java/org/apache/geode/internal/cache/PartitionedRegion.java