周海漢

2013.1.10

HBase 可以通過Region server的60030埠看到各區域的資訊。

新版的區域名字包含了尾巴上的encodeName，即用JenkinsHash計算後生成整形值轉成的10進位制字串，32位。其組成為“表名,起始行鍵,regionid.encodeName.”。ROOT表和第一個META表，及老版HRegion(0.20以前)，使用老的區域名。

原始碼如下：

HRegionInfo.java (srcmainjavaorgapachehadoophbase) 25868 2012/11/15

/**
   * Make a region name of passed parameters.
   * @param tableName
   * @param startKey Can be null
   * @param id Region id (Usually timestamp from when region was created).
   * @param newFormat should we create the region name in the new format
   *                  (such that it contains its encoded name?).
   * @return Region name made of passed tableName, startKey and id
   */
  public static byte [] createRegionName(final byte [] tableName,
      final byte [] startKey, final byte [] id, boolean newFormat) {
    byte [] b = new byte [tableName.length + 2 + id.length +
       (startKey == null? 0: startKey.length) +
       (newFormat ? (MD5_HEX_LENGTH + 2) : 0)];

    int offset = tableName.length;
    System.arraycopy(tableName, 0, b, 0, offset);
    b[offset++] = DELIMITER;
    if (startKey != null && startKey.length > 0) {
      System.arraycopy(startKey, 0, b, offset, startKey.length);
      offset += startKey.length;
    }
    b[offset++] = DELIMITER;
    System.arraycopy(id, 0, b, offset, id.length);
    offset += id.length;
//新版增加一個Hash值
    if (newFormat) {
      //
      // Encoded name should be built into the region name.
      //
      // Use the region name thus far (namely, ,,)
      // to compute a MD5 hash to be used as the encoded name, and append
      // it to the byte buffer.
      //
      String md5Hash = MD5Hash.getMD5AsHex(b, 0, offset);
      byte [] md5HashBytes = Bytes.toBytes(md5Hash);

      if (md5HashBytes.length != MD5_HEX_LENGTH) {
        LOG.error("MD5-hash length mismatch: Expected=" + MD5_HEX_LENGTH +
                  "; Got=" + md5HashBytes.length);
      }

      // now append the bytes '..' to the end
      b[offset++] = ENC_SEPARATOR;
      System.arraycopy(md5HashBytes, 0, b, offset, MD5_HEX_LENGTH);
      offset += MD5_HEX_LENGTH;
      b[offset++] = ENC_SEPARATOR;
    }
 

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