HIVE-10815 随机选择HiveMetaStoreClient

https://issues.apache.org/jira/browse/HIVE-10815   目前cdh5.4.0版本的hive第一次连接的时候，固定是使用第一个，只有连接失败后，才随机选择。

HiveMetaStoreClient.java

// user wants file store based configuration
    if (conf.getVar(HiveConf.ConfVars.METASTOREURIS) != null) {
      String metastoreUrisString[] = conf.getVar(
          HiveConf.ConfVars.METASTOREURIS).split(",");
      metastoreUris = new URI[metastoreUrisString.length];
      try {
        int i = 0;
        for (String s : metastoreUrisString) {
          URI tmpUri = new URI(s);
          if (tmpUri.getScheme() == null) {
            throw new IllegalArgumentException("URI: " + s
                + " does not have a scheme");
          }
          metastoreUris[i++] = tmpUri;

        }
      } catch (IllegalArgumentException e) {
        throw (e);
      } catch (Exception e) {
        MetaStoreUtils.logAndThrowMetaException(e);
      }
    } else {
      LOG.error("NOT getting uris from conf");
      throw new MetaException("MetaStoreURIs not found in conf file");
    }

 
在重连的时候，随机把后面的交换到第一个

private void promoteRandomMetaStoreURI() {
    if (metastoreUris.length <= 1) {
      return;
    }
    Random rng = new Random();
    int index = rng.nextInt(metastoreUris.length - 1) + 1;
    URI tmp = metastoreUris[0];
    metastoreUris[0] = metastoreUris[index];
    metastoreUris[index] = tmp;
  }

HIVE-10815让metastore初始化的时候先打乱顺序