int pruneEntriesOlderThan(long timeToPruneBefore, QuotaObserverChore quotaObserverChore) {
    if (regionSizes == null) {
      return 0;
    }
    int numEntriesRemoved = 0;
    Iterator<Entry<RegionInfo, SizeSnapshotWithTimestamp>> iterator =
      regionSizes.entrySet().iterator();
    while (iterator.hasNext()) {
      RegionInfo regionInfo = iterator.next().getKey();
      long currentEntryTime = regionSizes.get(regionInfo).getTime();
      // do not prune the entries if table is in violation and
      // violation policy is disable to avoid cycle of enable/disable.
      // Please refer HBASE-22012 for more details.
      // prune entries older than time.
      if (
        currentEntryTime < timeToPruneBefore
          && !isInViolationAndPolicyDisable(regionInfo.getTable(), quotaObserverChore)
      ) {
        iterator.remove();
        numEntriesRemoved++;
      }
    }
    return numEntriesRemoved;
  }
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