@Override
  public void add(ExtendedCell cell, MemStoreSizing memstoreSizing) {
    doAddOrUpsert(cell, 0, memstoreSizing, true);
  }
Updates the wal with the lowest sequence id (oldest entry) that is still in memory
@param onlyIfMoreRecent a flag that marks whether to update the sequence id no matter what or
                        only if it is greater than the previous sequence id
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/AbstractMemStore.java