@RestrictedApi(explanation = "Should only be called in tests", link = "",
      allowedOnPath = ".*/src/test/.*")
  public long getLowestSequenceId(final byte[] encodedRegionName) {
    synchronized (this.tieLock) {
      Map<?, Long> m = this.flushingSequenceIds.get(encodedRegionName);
      long flushingLowest = m != null ? getLowestSequenceId(m) : Long.MAX_VALUE;
      m = this.lowestUnflushedSequenceIds.get(encodedRegionName);
      long unflushedLowest = m != null ? getLowestSequenceId(m) : HConstants.NO_SEQNUM;
      return Math.min(flushingLowest, unflushedLowest);
    }
  }
Returns the lowest unflushed sequence id for the region.
@return Lowest outstanding unflushed sequenceid for <code>encodedRegionName</code>. Will return
        {@link HConstants#NO_SEQNUM} when none.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/SequenceIdAccounting.java