long getLowestSequenceId(final byte[] encodedRegionName, final byte[] familyName) {
    ImmutableByteArray familyNameWrapper = ImmutableByteArray.wrap(familyName);
    synchronized (this.tieLock) {
      Map<ImmutableByteArray, Long> m = this.flushingSequenceIds.get(encodedRegionName);
      if (m != null) {
        Long lowest = m.get(familyNameWrapper);
        if (lowest != null) {
          return lowest;
        }
      }
      m = this.lowestUnflushedSequenceIds.get(encodedRegionName);
      if (m != null) {
        Long lowest = m.get(familyNameWrapper);
        if (lowest != null) {
          return lowest;
        }
      }
    }
    return HConstants.NO_SEQNUM;
  }
@return Lowest outstanding unflushed sequenceid for <code>encodedRegionname</code> and
        <code>familyName</code>. Returned sequenceid may be for an edit currently being
        flushed.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/SequenceIdAccounting.java