@Override
  public void completeCacheFlush(byte[] encodedRegionName, long maxFlushedSeqId) {
    this.sequenceIdAccounting.completeCacheFlush(encodedRegionName, maxFlushedSeqId);
  }
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