Metastore源码分析

本文基于hive-1.2.2源码
Metastore模块在metastore目录下

入口文件

metastore/src/java/org/apache/hadoop/hive/metastore/HiveMetaStore.java

流程分析

1.由main函数开始

public static void main(String[] args) throws Throwable {
...
  startMetaStoreThreads(conf, startLock, startCondition, startedServing);
  startMetaStore(cli.port, ShimLoader.getHadoopThriftAuthBridge(), conf, startLock,
  startCondition, startedServing);
...
}

可见执行了2个方法，先启动一些线程，然后启动MetaStore

2.startMetaStoreThreads是启动一些compactor线程，这里略过

3.主流程在startMetaStore中，可以发现
3.1.MetaStore使用thtift来处理RPC连接，支持TCompactProtocol和TBinaryProtocol协议
3.2.MetaStore可以开启sasl支持，sasl实现是基于kerberos，使用MetaStore节点的keytab登录
3.3.MetaStore默认处理类为HMSHandler(即baseHandler)

public static void startMetaStore(int port, HadoopThriftAuthBridge bridge,
  HiveConf conf, Lock startLock, Condition startCondition,
  AtomicBoolean startedServing) throws Throwable {
  ...
  boolean useFramedTransport = conf.getBoolVar(ConfVars.METASTORE_USE_THRIFT_FRAMED_TRANSPORT);
  boolean useCompactProtocol = conf.getBoolVar(ConfVars.METASTORE_USE_THRIFT_COMPACT_PROTOCOL);
  useSasl = conf.getBoolVar(HiveConf.ConfVars.METASTORE_USE_THRIFT_SASL);
  ...
  if (useCompactProtocol) {
    protocolFactory = new TCompactProtocol.Factory();
    inputProtoFactory = new TCompactProtocol.Factory(maxMessageSize, maxMessageSize);
  } else {
    protocolFactory = new TBinaryProtocol.Factory();
    inputProtoFactory = new TBinaryProtocol.Factory(true, true, maxMessageSize, maxMessageSize);
  }
  HMSHandler baseHandler = new HiveMetaStore.HMSHandler("new db based metaserver", conf,
      false);
  IHMSHandler handler = newRetryingHMSHandler(baseHandler, conf);
  ...
  saslServer = bridge.createServer(
        conf.getVar(HiveConf.ConfVars.METASTORE_KERBEROS_KEYTAB_FILE),
        conf.getVar(HiveConf.ConfVars.METASTORE_KERBEROS_PRINCIPAL));
  ...

4.跟入代码可以发现
4.1.thrift相关定义在

metastore/src/gen/thrift/gen-javabean/org/apache/hadoop/hive/metastore/api

这个包是自动生成的，其中ThriftHiveMetastore.java定义了Metastore对外暴露的接口
4.2.Metastore的数据库操作是在ObjectStore.java文件中，里面实现了thrift暴露的各种接口，Metastore操作数据库是通过jdo进行，使用datanucleus框架
4.3.jdo定义在

metastore/src/model/org/apache/hadoop/hive/metastore/model

其中package.jdo定义了对象和数据库的映射

鉴权

private void drop_database_core(RawStore ms,
    final String name, final boolean deleteData, final boolean cascade)
    throws NoSuchObjectException, InvalidOperationException, MetaException,
    IOException, InvalidObjectException, InvalidInputException {
    ...
    firePreEvent(new PreDropDatabaseEvent(db, this));
    ...
}
...
private void firePreEvent(PreEventContext event) throws MetaException {
  for (MetaStorePreEventListener listener : preListeners) {
    try {
      listener.onEvent(event);
    } catch (NoSuchObjectException e) {
      throw new MetaException(e.getMessage());
    } catch (InvalidOperationException e) {
      throw new MetaException(e.getMessage());
    }
  }
}

1.1.HiveMetaStore.java中，有一些关于事件的操作，如drop_database_core中，有firePreEvent，Metastore的鉴权是基于类似的事件来做的，由MetaStorePreEventListener抛出InvalidOperationException来实现鉴权
1.2.事件的定义在

metastore/src/java/org/apache/hadoop/hive/metastore/events

1.3.HiveMetaStore的鉴权配置请参考 Storage Based Authorization in the Metastore Server

Metric

public void alter_database(final String dbName, final Database db)
    throws NoSuchObjectException, TException, MetaException {
  startFunction("alter_database" + dbName);
  ...
}
...
private String startFunction(String function, String extraLogInfo) {
  incrementCounter(function);
  logInfo((getIpAddress() == null ? "" : "source:" + getIpAddress() + " ") +
      function + extraLogInfo);
  try {
    Metrics.startScope(function);
  } catch (IOException e) {
    LOG.debug("Exception when starting metrics scope"
        + e.getClass().getName() + " " + e.getMessage(), e);
  }
  return function;
}

HiveMetaStore.java中，很多操作中都有startFunction，该方法将向metric中添加操作执行信息

其他

1.Warehouse

metastore/src/java/org/apache/hadoop/hive/metastore/Warehouse.java

这个类是和hive实际存储(一般是hdfs)打交道的

2.HiveMetaStoreClient

metastore/src/java/org/apache/hadoop/hive/metastore/HiveMetaStoreClient.java

这个类是自带的MetaStore客户端