如何扩展Hive Metastore Thrift RPC服务接口

Posted 2022-12-13 咬定青松

Hive 在经历十几年的发展，已经获得广泛应用，随着版本升级，不同版本之间的协议接口会发生一些变化，尽管HMS在尽量保持向前兼容，但在大版本变更时，仍然不能保证完全兼容，比如HMS2到HMS3，有关索引（Index）相关的接口变成了约束（constraint），比如下图中左边是HMS3接口定义，右边是HMS2接口定义：

这样当使用Hive 2的Client去访问HMS 3 的服务时候，就会报无效方法（Invalid Method）异常，此时可以通过一个Hive Metastore代理服务来解决。

在具体介绍Hive Metastore代理服务前，需要了解下Hive Metastore服务处理流程：

HMSHandler baseHandler = new HiveMetaStore.HMSHandler("metaserver", conf,false);
IHMSHandler handler = newRetryingHMSHandler(baseHandler, conf);
TProcessor processor = new ThriftHiveMetastore.Processor<>(handler));
final TThreadPoolServer.Args serverArgs = new TThreadPoolServer
    .Args(serverTransport)
    .transportFactory(new TTransportFactory())
    .protocolFactory(new TBinaryProtocol.Factory())
    .processor(processor);


TServer server = new TThreadPoolServer(serverArgs);
server.setServerEventHandler(getServerEventHandler());
server.serve();

上述示例代码启动了Hive Metastore的服务，其中两个重要的组件：

• TThreadPoolServer：负责请求的监听和派遣

• TProcessor：负责执行各RPC接口的实现逻辑

TThreadPoolServer功能介绍

TThreadPoolServer主要负责请求的监听和派遣，当接收到新的请求时，在内部将每个client的请求放入Worker线程池，然后继续下一个请求的监听，而工作线程负责一对一处理每个client的请求，直至处理完毕：

#TThreadPoolServer.class
public class TThreadPoolServer extends TServer 
    //private ExecutorService executorService_;
    
    public void serve() 
        ...
        while(!this.stopped_) 
            TTransport client = this.serverTransport_.accept();
            TThreadPoolServer.WorkerProcess wp = new TThreadPoolServer.WorkerProcess(client);
            this.executorService_.execute(wp);
        
        ...
        this.executorService_.shutdown();
    
    ...
    private class WorkerProcess implements Runnable 
        //private TTransport client_;
        public void run() 
            do 
                if (eventHandler != null) 
                    eventHandler.processContext(connectionContext, inputTransport, outputTransport);
                
              while(!TThreadPoolServer.this.stopped_ && processor.process(inputProtocol, outputProtocol));
            if (this.client_.isOpen()) 
                this.client_.close();
            
         
     
  

TProcessor功能介绍

上面介绍了WorkerProcess的工作功能，TThreadPoolServer将每个客户端连接整体扔给TProcessor，没有介绍在其通过processor.process处理时候，如何定位每个不同的方法，实际上区分不同方法调用的逻辑同时也是TProcessor负责的，以Processor为例，定义了所支持的接口映射：

#ThriftHiveMetastore.class
public static class Processor<I extends ThriftHiveMetastore.Iface> extends com.facebook.fb303.FacebookService.Processor<I> implements TProcessor 
    private static final Logger LOGGER = LoggerFactory.getLogger(ThriftHiveMetastore.Processor.class.getName());


    public Processor(I iface) 
        super(iface, getProcessMap(new HashMap()));
    


    //Note:processMap
    protected Processor(I iface, Map<String, ProcessFunction<I, ? extends TBase>> processMap) 
        super(iface, getProcessMap(processMap));
    


    private static <I extends ThriftHiveMetastore.Iface> Map<String, ProcessFunction<I, ? extends TBase>> getProcessMap(Map<String, ProcessFunction<I, ? extends TBase>> processMap) 
        processMap.put("create_catalog", new ThriftHiveMetastore.Processor.create_catalog());
        processMap.put("alter_catalog", new ThriftHiveMetastore.Processor.alter_catalog());
        processMap.put("get_catalog", new ThriftHiveMetastore.Processor.get_catalog());
        processMap.put("get_catalogs", new ThriftHiveMetastore.Processor.get_catalogs());
        processMap.put("drop_catalog", new ThriftHiveMetastore.Processor.drop_catalog());
        processMap.put("create_database", new ThriftHiveMetastore.Processor.create_database());
        processMap.put("get_database", new ThriftHiveMetastore.Processor.get_database());
        processMap.put("drop_database", new ThriftHiveMetastore.Processor.drop_database());
        ...
    
 

也就是凡是登记在processMap的方法才能被识别，否则都会报异常，这个逻辑可以在Processor的父类TBaseProcessor中得知：

public abstract class TBaseProcessor<I> implements TProcessor 
    private final I iface;
    private final Map<String, ProcessFunction<I, ? extends TBase>> processMap;


    protected TBaseProcessor(I iface, Map<String, ProcessFunction<I, ? extends TBase>> processFunctionMap) 
        this.iface = iface;
        this.processMap = processFunctionMap;
    


    public Map<String, ProcessFunction<I, ? extends TBase>> getProcessMapView() 
        return Collections.unmodifiableMap(this.processMap);
    
    
    public boolean process(TProtocol in, TProtocol out) throws TException 
        TMessage msg = in.readMessageBegin();
        ProcessFunction fn = (ProcessFunction)this.processMap.get(msg.name);
        if (fn == null) 
            TProtocolUtil.skip(in, (byte)12);
            in.readMessageEnd();
            TApplicationException x = new TApplicationException(1, "Invalid method name: '" + msg.name + "'");
            out.writeMessageBegin(new TMessage(msg.name, (byte)3, msg.seqid));
            x.write(out);
            out.writeMessageEnd();
            out.getTransport().flush();
            return true;
         else 
            fn.process(msg.seqid, in, out, this.iface);
            return true;
        

在process方法中，根据客户端调用传来的方法名称去查找processMap方法映射，如果找不到就报异常。如何添加非注册方法呢？观察Processor的构造方法：

#ThriftHiveMetastore.class
public static class Processor<I extends ThriftHiveMetastore.Iface> extends com.facebook.fb303.FacebookService.Processor<I> implements TProcessor 
    private static final Logger LOGGER = LoggerFactory.getLogger(ThriftHiveMetastore.Processor.class.getName());


    public Processor(I iface) 
        super(iface, getProcessMap(new HashMap()));
    


    //Note:processMap
    protected Processor(I iface, Map<String, ProcessFunction<I, ? extends TBase>> processMap) 
        super(iface, getProcessMap(processMap));
    
    ...
  

虽然可以传入processMap，但是该构造方法是protected，不允许直接创建对象 ，只能通过继承来扩展，比如这样：

public static class MetastoreProcessor<I extends ThriftHiveMetastore.Iface> extends ThriftHiveMetastore.Processor 


    private static final Logger LOGGER = LoggerFactory.getLogger(MetastoreProcess.class.getName());


    public MetastoreProcess(I iface) 
        super(iface, getProcessMap(new HashMap<String, ProcessFunction<I, ? extends TBase>>()));
    


    protected MetastoreProcess(I iface, Map<String, org.apache.thrift.ProcessFunction<I, ? extends org.apache.thrift.TBase>> processMap) 
        super(iface, getProcessMap(processMap));
    


    private static <I extends ThriftHiveMetastore.Iface> Map<String, org.apache.thrift.ProcessFunction<I, ? extends org.apache.thrift.TBase>> getProcessMap(Map<String, org.apache.thrift.ProcessFunction<I, ? extends org.apache.thrift.TBase>> processMap) 
        processMap.put("add_index", new add_index());
        processMap.put("alter_index", new alter_index());
        processMap.put("drop_index_by_name", new drop_index_by_name());
        processMap.put("get_index_by_name", new get_index_by_name());
        processMap.put("get_indexes", new get_indexes());
        processMap.put("get_index_names", new get_index_names());
        return processMap;
    

然后修改TProcessor实例，重建服务：

HMSHandler baseHandler = new HiveMetaStore.HMSHandler("metaserver", conf,false);
IHMSHandler handler = newRetryingHMSHandler(baseHandler, conf);
TProcessor processor = new MetastoreProcessor<>(handler));
final TThreadPoolServer.Args serverArgs = new TThreadPoolServer
    .Args(serverTransport)
    .transportFactory(new TTransportFactory())
    .protocolFactory(new TBinaryProtocol.Factory())
    .processor(processor);