private SingleStoreFileWriter getHistoricalFileWriter() throws IOException {
    if (historicalFileWriter == null) {
      historicalFileWriter =
        new SingleStoreFileWriter(fs, historicalFilePath, conf, cacheConf, bloomType, maxKeys,
          favoredNodes, fileContext, shouldDropCacheBehind, compactedFilesSupplier);
    }
    return historicalFileWriter;
  }
@param dir Directory to create file in.
@return random filename inside passed <code>dir</code>
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/StoreFileWriter.java