public void addRegionSize(RegionInfo hri, long size, long time) {
    if (regionSizes == null) {
      return;
    }
    regionSizes.put(hri, new SizeSnapshotWithTimestamp(size, time));
  }
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