@Override
  public Long startCacheFlush(byte[] encodedRegionName, Set<byte[]> families) {
    return this.sequenceIdAccounting.startCacheFlush(encodedRegionName, families);
  }
Used to initialize the WAL. Usually just call rollWriter to create the first log writer.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/wal/AbstractFSWAL.java