public Map<RegionInfo, Long> snapshotRegionSizes() {
    if (regionSizes == null) {
      return EMPTY_MAP;
    }

    Map<RegionInfo, Long> copy = new HashMap<>();
    for (Entry<RegionInfo, SizeSnapshotWithTimestamp> entry : regionSizes.entrySet()) {
      copy.put(entry.getKey(), entry.getValue().getSize());
    }
    return copy;
  }
Holds the size of a region at the given time, millis since the epoch.
hbase-server/src/main/java/org/apache/hadoop/hbase/quotas/MasterQuotaManager.java