private void checkLowReplication(long now) {
    try {
      for (Entry<WAL, RollController> entry : wals.entrySet()) {
        WAL wal = entry.getKey();
        boolean needRollAlready = entry.getValue().needsRoll(now);
        if (needRollAlready || !(wal instanceof AbstractFSWAL)) {
          continue;
        }
        ((AbstractFSWAL<?>) wal).checkLogLowReplication(checkLowReplicationInterval);
      }
    } catch (Throwable e) {
      LOG.warn("Failed checking low replication", e);
    }
  }
we need to check low replication in period, see HBASE-18132
hbase-server/src/main/java/org/apache/hadoop/hbase/wal/AbstractWALRoller.java