private Path createStagingDir(Path baseDir, User user, TableName tableName) throws IOException {
    String tblName = tableName.getNameAsString().replace(":", UNDERSCORE);
    int RANDOM_WIDTH = 320;
    int RANDOM_RADIX = 32;
    String doubleUnderScore = UNDERSCORE + UNDERSCORE;
    String randomDir = user.getShortName() + doubleUnderScore + tblName + doubleUnderScore
      + (new BigInteger(RANDOM_WIDTH, ThreadLocalRandom.current()).toString(RANDOM_RADIX));
    return createStagingDir(baseDir, user, randomDir);
  }
Number of hfiles to copy per thread during replication
hbase-server/src/main/java/org/apache/hadoop/hbase/replication/regionserver/HFileReplicator.java