public long getEstimatedLocalBucketSize(Set<Integer> bucketIds) {
    long size = 0;
    for (Integer bid : bucketIds) {
      BucketRegion br = localBucket2RegionMap.get(bid);
      if (br != null) {
        size += br.getEstimatedLocalSize();
      }
    }
    return size;
  }
a fast estimate of total bucket size
geode-core/src/main/java/org/apache/geode/internal/cache/PartitionedRegionDataStore.java