@Override
  public Iterable<Entry<RegionInfo, Long>> filterBySubject(TableName table) {
    rlock.lock();
    try {
      return regionUsage.entrySet().stream()
        .filter(entry -> table.equals(entry.getKey().getTable())).collect(Collectors.toList());
    } finally {
      rlock.unlock();
    }
  }
Fetches any serialized snapshot sizes from the quota table for the {@code tn} provided. Any
malformed records are skipped with a warning printed out.
hbase-server/src/main/java/org/apache/hadoop/hbase/quotas/TableQuotaSnapshotStore.java