int sizeEstimate() {
    boolean isClient = imageState.isClient();
    if (isClient) {
      throw new UnsupportedOperationException("Method not supported on a client");
    }
    return entryCount(null, true);
  }
returns an estimate of the number of entries in this region. This method should be preferred
over size() for hdfs regions where an accurate size is not needed. This method is not supported
on a client

@return the estimated size of this region
geode-core/src/main/java/org/apache/geode/internal/cache/LocalRegion.java