一、HQL是如何转换为MR任务的

1、Hive的核心组成介绍

#用户接口：Client
	CLI（command-line interface）、JDBC/ODBC(jdbc访问hive)、WEBUI（浏览器访问hive）
#元数据：Metastore
	元数据包括：表名、表所属的数据库（默认是default）、表的拥有者、列/分区字段、表的类型（是否是外部表）、表的数据所在目录等；
	默认存储在自带的derby数据库中，推荐使用MySQL存储Metastore
#Hadoop
	使用HDFS进行存储，使用MapReduce进行计算。
#驱动器：Driver
#解析器（SQL Parser）
	将SQL字符串转换成抽象语法树AST，这一步一般都用第三方工具库完成，比如antlr；对AST进行语法分析，比如表是否存在、字段是否存在、SQL语义是否有误。
#编译器（Physical Plan）
	将AST编译生成逻辑执行计划。
#优化器（Query Optimizer）
	对逻辑执行计划进行优化。
#执行器（Execution）
	把逻辑执行计划转换成可以运行的物理计划。对于Hive来说，就是MR/Spark。
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2、HQL转换为MR任务流程说明

1）进入程序，利用Antlr框架定义HQL的语法规则，对HQL完成词法语法解析，将HQL转换为AST（抽象语法树）；

2）遍历AST，抽象出查询的基本组成单元QueryBlock（查询块），可以理解为最小的查询执行单元；

3）遍历QueryBlock，将其转换为OperatorTree（操作树，也就是逻辑执行计划）可以理解为不可拆分的一个逻辑执行单元；

4）使用逻辑优化器对OperatorTree（操作树）进行逻辑优化。例如合并不必要的ReduceSinkOperator，减少Shuffle数据量；

5）遍历OperatorTree，转换为TaskTree。也就是翻译为MR任务的流程，将逻辑执行计划转换为物理执行计划；

6）使用物理优化器对TaskTree进行物理优化

7）生成最终的执行计划，提交任务到Hadoop集群运行

二、HQL转换为MR源码详细解读

1、HQL转换为MR源码整体流程介绍

2、程序入口–CliDriver

我们执行一个HQL语句通常有以下几种方式：

$HIVE_HOME/bin/hive 进入客户端，然后执行HQL；

$HIVE_HOME/bin/hive -e “hql”;

$HIVE_HOME/bin/hive -f hive.sql;

先开启hiveserver2服务端，然后通过JDBC方式连接远程提交HQL。

可以知道我们执行HQL主要依赖于HIVE_HOME/bin/hive和HIVE_HOME/bin/hiveserver2两种脚本来实现提交HQL，而在这两个脚本中，最终启动的JAVA进程的主类为”org.apache.hadoop.hive.cli.CliDriver“，所以其实hive程序的入口就是CliDriver类。

3、HQL的读取与参数解析

3.1、找到"CLiDriver"这个类的”main“方法

public static void main(String[] args) throws Exception {
    int ret = new CliDriver().run(args);
    System.exit(ret);
  }
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3.2、主类的run方法

 public  int run(String[] args) throws Exception {
    OptionsProcessor oproc = new OptionsProcessor();
    //解析系统参数
    if (!oproc.process_stage1(args)) {
      return 1;
    }
    ... ...
    CliSessionState ss = new CliSessionState(new HiveConf(SessionState.class));
    //标准输入输出以及错误输出流的定义,后续需要输入HQL以及打印控制台信息
    ss.in = System.in;
    try {
      ss.out = new PrintStream(System.out, true, "UTF-8");
      ss.info = new PrintStream(System.err, true, "UTF-8");
      ss.err = new CachingPrintStream(System.err, true, "UTF-8");
    } catch (UnsupportedEncodingException e) {
      return 3;
    }
    //解析用户参数,包含"-e -f -v -database"等等
    if (!oproc.process_stage2(ss)) {
      return 2;
    }
    ... ...
    // execute cli driver work
    try {
      return executeDriver(ss, conf, oproc);
    } finally {
      ss.resetThreadName();
      ss.close();
    }
  }
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3.3、executeDriver方法

private int executeDriver(CliSessionState ss, HiveConf conf, OptionsProcessor oproc) throws Exception {
    CliDriver cli = new CliDriver();
    cli.setHiveVariables(oproc.getHiveVariables());
    // use the specified database if specified
    cli.processSelectDatabase(ss);
    // Execute -i init files (always in silent mode)
    cli.processInitFiles(ss);

    if (ss.execString != null) {
      int cmdProcessStatus = cli.processLine(ss.execString);
      return cmdProcessStatus;
    }

    ... ...

    setupConsoleReader();

    String line;
    int ret = 0;
    String prefix = "";
    String curDB = getFormattedDb(conf, ss);
    String curPrompt = prompt + curDB;
    String dbSpaces = spacesForString(curDB);

    //读取客户端的输入HQL 
    while ((line = reader.readLine(curPrompt + "> ")) != null) {
      if (!prefix.equals("")) {
        prefix += '\n';
      }
      if (line.trim().startsWith("--")) {
        continue;
      }
      //以按照“;”分割的方式解析
      if (line.trim().endsWith(";") && !line.trim().endsWith("\\;")) {
        line = prefix + line;
        ret = cli.processLine(line, true);
        prefix = "";
        curDB = getFormattedDb(conf, ss);
        curPrompt = prompt + curDB;
        dbSpaces = dbSpaces.length() == curDB.length() ? dbSpaces : spacesForString(curDB);
      } else {
        prefix = prefix + line;
        curPrompt = prompt2 + dbSpaces;
        continue;
      }
    }

    return ret;
  }
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3.4、processLine方法

 public int processLine(String line, boolean allowInterrupting) {
    SignalHandler oldSignal = null;
    Signal interruptSignal = null;
    ... ...
    try {
      int lastRet = 0, ret = 0;

      // we can not use "split" function directly as ";" may be quoted
      List<String> commands = splitSemiColon(line);

      String command = "";
      for (String oneCmd : commands) {

        if (StringUtils.endsWith(oneCmd, "\\")) {
          command += StringUtils.chop(oneCmd) + ";";
          continue;
        } else {
          command += oneCmd;
        }
        if (StringUtils.isBlank(command)) {
          continue;
        }

//解析单行HQL
        ret = processCmd(command);
        command = "";
        lastRet = ret;
        boolean ignoreErrors = HiveConf.getBoolVar(conf, HiveConf.ConfVars.CLIIGNOREERRORS);
        if (ret != 0 && !ignoreErrors) {
          return ret;
        }
      }
      return lastRet;
    } finally {
      // Once we are done processing the line, restore the old handler
      if (oldSignal != null && interruptSignal != null) {
        Signal.handle(interruptSignal, oldSignal);
      }
    }
  }
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3.5、processCmd方法

public int processCmd(String cmd) {
    CliSessionState ss = (CliSessionState) SessionState.get();
    
    ... ...

    //1.如果命令为"quit"或者"exit",则退出
    if (cmd_trimmed.toLowerCase().equals("quit") || cmd_trimmed.toLowerCase().equals("exit")) {

      // if we have come this far - either the previous commands
      // are all successful or this is command line. in either case
      // this counts as a successful run
      ss.close();
      System.exit(0);

    //2.如果命令为"source"开头,则表示执行HQL文件,继续读取文件并解析
    } else if (tokens[0].equalsIgnoreCase("source")) {
      String cmd_1 = getFirstCmd(cmd_trimmed, tokens[0].length());
      cmd_1 = new VariableSubstitution(new HiveVariableSource() {
        @Override
        public Map<String, String> getHiveVariable() {
          return SessionState.get().getHiveVariables();
        }
      }).substitute(ss.getConf(), cmd_1);

      File sourceFile = new File(cmd_1);
      if (! sourceFile.isFile()){
        console.printError("File: "+ cmd_1 + " is not a file.");
        ret = 1;
      } else {
        try {
          ret = processFile(cmd_1);
        } catch (IOException e) {
          console.printError("Failed processing file "+ cmd_1 +" "+ e.getLocalizedMessage(),
            stringifyException(e));
          ret = 1;
        }
      }

      //3.如果命令以"!"开头,则表示用户需要执行Linux命令
    } else if (cmd_trimmed.startsWith("!")) {
      // for shell commands, use unstripped command
      String shell_cmd = cmd.trim().substring(1);
      shell_cmd = new VariableSubstitution(new HiveVariableSource() {
        @Override
        public Map<String, String> getHiveVariable() {
          return SessionState.get().getHiveVariables();
        }
      }).substitute(ss.getConf(), shell_cmd);

      // shell_cmd = "/bin/bash -c \'" + shell_cmd + "\'";
      try {
        ShellCmdExecutor executor = new ShellCmdExecutor(shell_cmd, ss.out, ss.err);
        ret = executor.execute();
        if (ret != 0) {
          console.printError("Command failed with exit code = " + ret);
        }
      } catch (Exception e) {
        console.printError("Exception raised from Shell command " + e.getLocalizedMessage(),
            stringifyException(e));
        ret = 1;
      }

      //4.以上三者都不是,则认为用户输入的为"select ..."正常的增删改查HQL语句,则进行HQL解析
    }  else {
      try {

        try (CommandProcessor proc = CommandProcessorFactory.get(tokens, (HiveConf) conf)) {
          if (proc instanceof IDriver) {
            // Let Driver strip comments using sql parser
            ret = processLocalCmd(cmd, proc, ss);
          } else {
            ret = processLocalCmd(cmd_trimmed, proc, ss);
          }
        }
      } catch (SQLException e) {
        console.printError("Failed processing command " + tokens[0] + " " + e.getLocalizedMessage(),
          org.apache.hadoop.util.StringUtils.stringifyException(e));
        ret = 1;
      }
      catch (Exception e) {
        throw new RuntimeException(e);
      }
    }

    ss.resetThreadName();
    return ret;
  }
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3.6、processLocalCmd方法

 int processLocalCmd(String cmd, CommandProcessor proc, CliSessionState ss) {
    boolean escapeCRLF = HiveConf.getBoolVar(conf, HiveConf.ConfVars.HIVE_CLI_PRINT_ESCAPE_CRLF);
    int ret = 0;

    if (proc != null) {
      if (proc instanceof IDriver) {
        IDriver qp = (IDriver) proc;
        PrintStream out = ss.out;

        //获取系统时间作为开始时间,以便后续计算HQL执行时长
        long start = System.currentTimeMillis();
        if (ss.getIsVerbose()) {
          out.println(cmd);
        }

        //HQL执行的核心方法
        ret = qp.run(cmd).getResponseCode();
        if (ret != 0) {
          qp.close();
          return ret;
        }

        // query has run capture the time
        //获取系统时间作为结束时间,以便后续计算HQL执行时长
        long end = System.currentTimeMillis();
        double timeTaken = (end - start) / 1000.0;

        ArrayList<String> res = new ArrayList<String>();

        //打印头信息
        printHeader(qp, out);

        // print the results,包含结果集并获取抓取到数据的条数
        int counter = 0;
        try {
          if (out instanceof FetchConverter) {
            ((FetchConverter) out).fetchStarted();
          }
          while (qp.getResults(res)) {
            for (String r : res) {
                  if (escapeCRLF) {
                    r = EscapeCRLFHelper.escapeCRLF(r);
                  }
              out.println(r);
            }
            counter += res.size();
            res.clear();
            if (out.checkError()) {
              break;
            }
          }
        } catch (IOException e) {
          console.printError("Failed with exception " + e.getClass().getName() + ":" + e.getMessage(),
              "\n" + org.apache.hadoop.util.StringUtils.stringifyException(e));
          ret = 1;
        }

        qp.close();

        if (out instanceof FetchConverter) {
          ((FetchConverter) out).fetchFinished();
        }

        //打印HQL执行时间以及抓取数据的条数（经常使用Hive的同学是否觉得这句很熟悉呢，其实就是执行完一个HQL最后打印的那句话）
        console.printInfo(
            "Time taken: " + timeTaken + " seconds" + (counter == 0 ? "" : ", Fetched: " + counter + " row(s)"));
      } else {
        String firstToken = tokenizeCmd(cmd.trim())[0];
        String cmd_1 = getFirstCmd(cmd.trim(), firstToken.length());

        if (ss.getIsVerbose()) {
          ss.out.println(firstToken + " " + cmd_1);
        }
        CommandProcessorResponse res = proc.run(cmd_1);
        if (res.getResponseCode() != 0) {
          ss.out
              .println("Query returned non-zero code: " + res.getResponseCode() + ", cause: " + res.getErrorMessage());
        }
        if (res.getConsoleMessages() != null) {
          for (String consoleMsg : res.getConsoleMessages()) {
            console.printInfo(consoleMsg);
          }
        }
        ret = res.getResponseCode();
      }
    }

    return ret;
  }
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3.7、qp.run(cmd)方法

点击进入”run“方法，该方法为IDriver接口的抽象方法，此处实际调用的是“org.apache.hadoop.hive.ql.Driver”类中的“run”方法，找到“Driver”类中的“run”方法。

public CommandProcessorResponse run(String command) {
    return run(command, false);
  }

public CommandProcessorResponse run(String command, boolean alreadyCompiled) {

    try {
      runInternal(command, alreadyCompiled);
      return createProcessorResponse(0);
    } catch (CommandProcessorResponse cpr) {
      ... ...
    }
    
  }
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3.8、runInternal方法

 private void runInternal(String command, boolean alreadyCompiled) throws CommandProcessorResponse {
    errorMessage = null;
    SQLState = null;
    downstreamError = null;
    LockedDriverState.setLockedDriverState(lDrvState);

    lDrvState.stateLock.lock();
    ... ...
      PerfLogger perfLogger = null;
      if (!alreadyCompiled) {
        // compile internal will automatically reset the perf logger
        //1.编译HQL语句
        compileInternal(command, true);
        // then we continue to use this perf logger
        perfLogger = SessionState.getPerfLogger();
      }
      ... ...
      
      try {
        //2.执行
        execute();
      } catch (CommandProcessorResponse cpr) {
        rollback(cpr);
        throw cpr;
      }
      isFinishedWithError = false;
    } 
  }
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4、HQL生成AST（抽象语法树）

4.1、compileInternal方法

 private void compileInternal(String command, boolean deferClose) throws CommandProcessorResponse {
    Metrics metrics = MetricsFactory.getInstance();
    if (metrics != null) {
      metrics.incrementCounter(MetricsConstant.WAITING_COMPILE_OPS, 1);
}

    … …

    if (compileLock == null) {
      throw createProcessorResponse(ErrorMsg.COMPILE_LOCK_TIMED_OUT.getErrorCode());
    }

    try {
      compile(command, true, deferClose);
    } catch (CommandProcessorResponse cpr) {
      try {
        releaseLocksAndCommitOrRollback(false);
      } catch (LockException e) {
        LOG.warn("Exception in releasing locks. " + org.apache.hadoop.util.StringUtils.stringifyException(e));
      }
      throw cpr;
    } 
  }
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4.2、compile方法

private void compile(String command, boolean resetTaskIds, boolean deferClose) throws CommandProcessorResponse {
    PerfLogger perfLogger = SessionState.getPerfLogger(true);
    perfLogger.PerfLogBegin(CLASS_NAME, PerfLogger.DRIVER_RUN);
    perfLogger.PerfLogBegin(CLASS_NAME, PerfLogger.COMPILE);
    lDrvState.stateLock.lock();

    ... ...

	 //HQL生成AST
      ASTNode tree;
      try {
        tree = ParseUtils.parse(command, ctx);
      } catch (ParseException e) {
        parseError = true;
        throw e;
      } finally {
        hookRunner.runAfterParseHook(command, parseError);
      }
}
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4.3、parse方法

 /** Parses the Hive query. */
  public static ASTNode parse(String command, Context ctx) throws ParseException {
    return parse(command, ctx, null);
  }
  
  public static ASTNode parse(
      String command, Context ctx, String viewFullyQualifiedName) throws ParseException {
    ParseDriver pd = new ParseDriver();
    ASTNode tree = pd.parse(command, ctx, viewFullyQualifiedName);
    tree = findRootNonNullToken(tree);
    handleSetColRefs(tree);
    return tree;
  }
  
  public ASTNode parse(String command, Context ctx, String viewFullyQualifiedName)
      throws ParseException {
    if (LOG.isDebugEnabled()) {
      LOG.debug("Parsing command: " + command);
    }

    //1.构建词法解析器
    HiveLexerX lexer = new HiveLexerX(new ANTLRNoCaseStringStream(command));

    //2.将HQL中的关键词替换为Token
    TokenRewriteStream tokens = new TokenRewriteStream(lexer);
    if (ctx != null) {
      if (viewFullyQualifiedName == null) {
        // Top level query
        ctx.setTokenRewriteStream(tokens);
      } else {
        // It is a view
        ctx.addViewTokenRewriteStream(viewFullyQualifiedName, tokens);
      }
      lexer.setHiveConf(ctx.getConf());
    }
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说明：Antlr框架。Hive使用Antlr实现SQL的词法和语法解析。Antlr是一种语言识别的工具，可以用来构造领域语言。使用Antlr构造特定的语言只需要编写一个语法文件，定义词法和语法替换规则即可，Antlr完成了词法分析、语法分析、语义分析、中间代码生成的过程。

​ hive中语法规则的定义文件在0.10版本以前是一个Hive.g一个文件，随着语法规则越来越复杂，由语法规则生成的Java解析类可能超过Java类文件的最大上限，0.11版本将Hive.g拆成了5个文件，词法规则HiveLexer.g和语法规则的4个文件SelectClauseParser.g、FromClauseParser.g、IdentifiersParser.g、HiveParser.g。

HiveParser parser = new HiveParser(tokens);
    if (ctx != null) {
      parser.setHiveConf(ctx.getConf());
    }
    parser.setTreeAdaptor(adaptor);
    HiveParser.statement_return r = null;
    try {
      //3.进行语法解析，生成最终的AST
      r = parser.statement();
    } catch (RecognitionException e) {
      e.printStackTrace();
      throw new ParseException(parser.errors);
    }

    if (lexer.getErrors().size() == 0 && parser.errors.size() == 0) {
      LOG.debug("Parse Completed");
    } else if (lexer.getErrors().size() != 0) {
      throw new ParseException(lexer.getErrors());
    } else {
      throw new ParseException(parser.errors);
    }

    ASTNode tree = (ASTNode) r.getTree();
    tree.setUnknownTokenBoundaries();
    return tree;
  }
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说明：例如HQL语句为：

FROM
( 
  SELECT
    p.datekey datekey,
    p.userid userid,
    c.clienttype
  FROM
    detail.usersequence_client c
    JOIN fact.orderpayment p ON p.orderid = c.orderid
    JOIN default.user du ON du.userid = p.userid
  WHERE p.datekey = 20131118 
) base
INSERT OVERWRITE TABLE `test`.`customer_kpi`
SELECT
  base.datekey,
  base.clienttype,
  count(distinct base.userid) buyer_count
GROUP BY base.datekey, base.clienttype
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生成对应的AST抽象语法树为：

5、对AST进一步解析

接下来的步骤包括：

1）将AST转换为QueryBlock进一步转换为OperatorTree；

2）对OperatorTree进行逻辑优化（LogicalOptimizer）；

3）将OperatorTree转换为TaskTree（任务树）；

4）对TaskTree进行物理优化（PhysicalOptimizer）。

之所以将这4个步骤写在一起，是因为这几个步骤在源码中存在于一个方法中。

5.1、compile方法

 private void compile(String command, boolean resetTaskIds, boolean deferClose) throws CommandProcessorResponse {
    PerfLogger perfLogger = SessionState.getPerfLogger(true);
    perfLogger.PerfLogBegin(CLASS_NAME, PerfLogger.DRIVER_RUN);
    perfLogger.PerfLogBegin(CLASS_NAME, PerfLogger.COMPILE);
    lDrvState.stateLock.lock();

    ... ...

	 //HQL生成AST
      ASTNode tree;
      try {
        tree = ParseUtils.parse(command, ctx);
      } catch (ParseException e) {
        parseError = true;
        throw e;
      } finally {
        hookRunner.runAfterParseHook(command, parseError);
      }

      // Do semantic analysis and plan generation
      BaseSemanticAnalyzer sem = SemanticAnalyzerFactory.get(queryState, tree);

      if (!retrial) {
        openTransaction();
        generateValidTxnList();
      }

		 //进一步解析抽象语法树
      sem.analyze(tree, ctx);
}
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5.2、analyze方法

  public void analyze(ASTNode ast, Context ctx) throws SemanticException {
    initCtx(ctx);
    init(true);
    analyzeInternal(ast);
  }
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5.3、analyzeInternal方法

  public abstract void analyzeInternal(ASTNode ast) throws SemanticException;
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此方法为"org.apache.hadoop.hive.ql.parse.BaseSemanticAnalyzer"抽象类的抽象方法，我们进入实现类“org.apache.hadoop.hive.ql.parse.SemanticAnalyzer”的analyzeInternal方法。

 public void analyzeInternal(ASTNode ast) throws SemanticException {
    analyzeInternal(ast, new PlannerContextFactory() {
      @Override
      public PlannerContext create() {
        return new PlannerContext();
      }
    });
  }
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5.4、继续调用重载的analyzeInternal方法

注意：该段源码中出现的“1,2,3,4…11”均为源码所定义步骤，该方法代码虽然很长，但是由于存在官方提供的步骤注释，其实读懂并不难。

void analyzeInternal(ASTNode ast, PlannerContextFactory pcf) throws SemanticException {
    LOG.info("Starting Semantic Analysis");
    // 1. Generate Resolved Parse tree from syntax tree
    boolean needsTransform = needsTransform();
    //change the location of position alias process here
    processPositionAlias(ast);
    PlannerContext plannerCtx = pcf.create();
//处理AST，转换为QueryBlock
    if (!genResolvedParseTree(ast, plannerCtx)) {
      return;
    }

      ... ...

    // 2. Gen OP Tree from resolved Parse Tree
    Operator sinkOp = genOPTree(ast, plannerCtx);

    // 3. Deduce Resultset Schema:定义输出数据的Schema
… …

    // 4. Generate Parse Context for Optimizer & Physical compiler
    copyInfoToQueryProperties(queryProperties);
    ParseContext pCtx = new ParseContext(queryState, opToPartPruner, opToPartList, topOps,
        new HashSet<JoinOperator>(joinContext.keySet()),
        new HashSet<SMBMapJoinOperator>(smbMapJoinContext.keySet()),
        loadTableWork, loadFileWork, columnStatsAutoGatherContexts, ctx, idToTableNameMap, destTableId, uCtx,
        listMapJoinOpsNoReducer, prunedPartitions, tabNameToTabObject, opToSamplePruner,
        globalLimitCtx, nameToSplitSample, inputs, rootTasks, opToPartToSkewedPruner,
        viewAliasToInput, reduceSinkOperatorsAddedByEnforceBucketingSorting,
        analyzeRewrite, tableDesc, createVwDesc, materializedViewUpdateDesc,
        queryProperties, viewProjectToTableSchema, acidFileSinks);

      ... ...

    // 5. Take care of view creation：处理视图相关

… …

    // 6. Generate table access stats if required
    if (HiveConf.getBoolVar(this.conf, HiveConf.ConfVars.HIVE_STATS_COLLECT_TABLEKEYS)) {
      TableAccessAnalyzer tableAccessAnalyzer = new TableAccessAnalyzer(pCtx);
      setTableAccessInfo(tableAccessAnalyzer.analyzeTableAccess());
    }

    // 7. Perform Logical optimization：对操作树执行逻辑优化
    if (LOG.isDebugEnabled()) {
      LOG.debug("Before logical optimization\n" + Operator.toString(pCtx.getTopOps().values()));
    }
    
//创建优化器
    Optimizer optm = new Optimizer();
    optm.setPctx(pCtx);
    optm.initialize(conf);
//执行优化
    pCtx = optm.optimize();
    if (pCtx.getColumnAccessInfo() != null) {
      // set ColumnAccessInfo for view column authorization
      setColumnAccessInfo(pCtx.getColumnAccessInfo());
    }
    if (LOG.isDebugEnabled()) {
      LOG.debug("After logical optimization\n" + Operator.toString(pCtx.getTopOps().values()));
    }

    // 8. Generate column access stats if required - wait until column pruning
    // takes place during optimization
    boolean isColumnInfoNeedForAuth = SessionState.get().isAuthorizationModeV2()
        && HiveConf.getBoolVar(conf, HiveConf.ConfVars.HIVE_AUTHORIZATION_ENABLED);
    if (isColumnInfoNeedForAuth
        || HiveConf.getBoolVar(this.conf, HiveConf.ConfVars.HIVE_STATS_COLLECT_SCANCOLS)) {
      ColumnAccessAnalyzer columnAccessAnalyzer = new ColumnAccessAnalyzer(pCtx);
      // view column access info is carried by this.getColumnAccessInfo().
      setColumnAccessInfo(columnAccessAnalyzer.analyzeColumnAccess(this.getColumnAccessInfo()));
    }

    // 9. Optimize Physical op tree & Translate to target execution engine (MR,
    // TEZ..)：执行物理优化
    if (!ctx.getExplainLogical()) {
      TaskCompiler compiler = TaskCompilerFactory.getCompiler(conf, pCtx);
      compiler.init(queryState, console, db);
	   //compile为抽象方法，对应的实现类分别为MapReduceCompiler、TezCompiler和SparkCompiler
      compiler.compile(pCtx, rootTasks, inputs, outputs);
      fetchTask = pCtx.getFetchTask();
    }
    //find all Acid FileSinkOperatorS
    QueryPlanPostProcessor qp = new QueryPlanPostProcessor(rootTasks, acidFileSinks, ctx.getExecutionId());

    // 10. Attach CTAS/Insert-Commit-hooks for Storage Handlers

      ... ...

    LOG.info("Completed plan generation");

    // 11. put accessed columns to readEntity
    if (HiveConf.getBoolVar(this.conf, HiveConf.ConfVars.HIVE_STATS_COLLECT_SCANCOLS)) {
      putAccessedColumnsToReadEntity(inputs, columnAccessInfo);
    }

    if (isCacheEnabled && lookupInfo != null) {
      if (queryCanBeCached()) {
        QueryResultsCache.QueryInfo queryInfo = createCacheQueryInfoForQuery(lookupInfo);

        // Specify that the results of this query can be cached.
        setCacheUsage(new CacheUsage(
            CacheUsage.CacheStatus.CAN_CACHE_QUERY_RESULTS, queryInfo));
      }
    }
  }
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5.5、提交任务并执行3.8的第二步

 //2.执行
 execute();
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5.6、execute方法

 private void execute() throws CommandProcessorResponse {
    PerfLogger perfLogger = SessionState.getPerfLogger();
    perfLogger.PerfLogBegin(CLASS_NAME, PerfLogger.DRIVER_EXECUTE);

      ... ...

      //1.构建任务：根据任务树构建MrJob
      setQueryDisplays(plan.getRootTasks());
      int mrJobs = Utilities.getMRTasks(plan.getRootTasks()).size();
      int jobs = mrJobs + Utilities.getTezTasks(plan.getRootTasks()).size()
          + Utilities.getSparkTasks(plan.getRootTasks()).size();
      if (jobs > 0) {
        logMrWarning(mrJobs);
        console.printInfo("Query ID = " + queryId);
        console.printInfo("Total jobs = " + jobs);
      }
      

      perfLogger.PerfLogBegin(CLASS_NAME, PerfLogger.RUN_TASKS);
      // Loop while you either have tasks running, or tasks queued up
      while (driverCxt.isRunning()) {
        // Launch upto maxthreads tasks
        Task<? extends Serializable> task;
        while ((task = driverCxt.getRunnable(maxthreads)) != null) {

          //2.启动任务
          TaskRunner runner = launchTask(task, queryId, noName, jobname, jobs, driverCxt);
          if (!runner.isRunning()) {
            break;
          }
        }

        ... ...

    //打印结果中最后的OK
    if (console != null) {
      console.printInfo("OK");
    }
  }
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5.7、launchTask方法

private TaskRunner launchTask(Task<? extends Serializable> tsk, String queryId, boolean noName,
      String jobname, int jobs, DriverContext cxt) throws HiveException {
    if (SessionState.get() != null) {
      SessionState.get().getHiveHistory().startTask(queryId, tsk, tsk.getClass().getName());
    }
    if (tsk.isMapRedTask() && !(tsk instanceof ConditionalTask)) {
      if (noName) {
        conf.set(MRJobConfig.JOB_NAME, jobname + " (" + tsk.getId() + ")");
      }
      conf.set(DagUtils.MAPREDUCE_WORKFLOW_NODE_NAME, tsk.getId());
      Utilities.setWorkflowAdjacencies(conf, plan);
      cxt.incCurJobNo(1);
      console.printInfo("Launching Job " + cxt.getCurJobNo() + " out of " + jobs);
    }
    tsk.initialize(queryState, plan, cxt, ctx.getOpContext());
    TaskRunner tskRun = new TaskRunner(tsk);

    //添加启动任务
cxt.launching(tskRun);

    // Launch Task：根据是否可以并行来决定是否并行启动Task
    if (HiveConf.getBoolVar(conf, HiveConf.ConfVars.EXECPARALLEL) && tsk.canExecuteInParallel()) {
      // Launch it in the parallel mode, as a separate thread only for MR tasks
      if (LOG.isInfoEnabled()){
        LOG.info("Starting task [" + tsk + "] in parallel");
      }
      //可并行任务启动,实际上还是执行tskRun.runSequential();
      tskRun.start();
    } else {
      if (LOG.isInfoEnabled()){
        LOG.info("Starting task [" + tsk + "] in serial mode");
      }
      //不可并行任务,则按照序列顺序执行任务
      tskRun.runSequential();
    }
    return tskRun;
  }
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5.8、runSequential方法

 public void runSequential() {
    int exitVal = -101;
    try {
      exitVal = tsk.executeTask(ss == null ? null : ss.getHiveHistory());
    } catch (Throwable t) {
      if (tsk.getException() == null) {
        tsk.setException(t);
      }
      LOG.error("Error in executeTask", t);
    }
    result.setExitVal(exitVal);
    if (tsk.getException() != null) {
      result.setTaskError(tsk.getException());
    }
  }
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5.9、 executeTask方法

public int executeTask(HiveHistory hiveHistory) {
    try {
      this.setStarted();
      if (hiveHistory != null) {
        hiveHistory.logPlanProgress(queryPlan);
      }
      int retval = execute(driverContext);
      this.setDone();
      if (hiveHistory != null) {
        hiveHistory.logPlanProgress(queryPlan);
      }
      return retval;
    } catch (IOException e) {
      throw new RuntimeException("Unexpected error: " + e.getMessage(), e);
    }
  }
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5.10、 execute方法

 protected abstract int execute(DriverContext driverContext);
1

此时我们进入了一个抽象“org.apache.hadoop.hive.ql.exec.Task”的“execute”方法，我们则需要找到一个实现类的“execute”方法，此处我选择“org.apache.hadoop.hive.ql.exec.mr.MapRedTask”这个类。

public int execute(DriverContext driverContext) {

    Context ctx = driverContext.getCtx();
    boolean ctxCreated = false;

    try {
      
      ... ...

      if (!runningViaChild) {
        // since we are running the mapred task in the same jvm, we should update the job conf
        // in ExecDriver as well to have proper local properties.
        if (this.isLocalMode()) {
          // save the original job tracker
          ctx.setOriginalTracker(ShimLoader.getHadoopShims().getJobLauncherRpcAddress(job));
          // change it to local
          ShimLoader.getHadoopShims().setJobLauncherRpcAddress(job, "local");
        }
        // we are not running this mapred task via child jvm
        // so directly invoke ExecDriver

        //设置MR任务的InputFormat、OutputFormat等等这些MRJob的执行类
        int ret = super.execute(driverContext);

        // restore the previous properties for framework name, RM address etc.
        if (this.isLocalMode()) {
          // restore the local job tracker back to original
          ctx.restoreOriginalTracker();
        }
        return ret;
      }

      ... ...

      //构建执行MR任务的命令
      String isSilent = "true".equalsIgnoreCase(System
          .getProperty("test.silent")) ? "-nolog" : "";

      String jarCmd = hiveJar + " " + ExecDriver.class.getName() + libJarsOption;

      String cmdLine = hadoopExec + " jar " + jarCmd + " -plan "
          + planPath.toString() + " " + isSilent + " " + hiveConfArgs;

      ... ...

      // Run ExecDriver in another JVM
      executor = Runtime.getRuntime().exec(cmdLine, env, new File(workDir));
  }
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三、Hive源码Debug介绍

1、Debug环境准备

1.1、源码包

下载hive3.1.2版本。编译，建议在linux环境下编译，然后将整个编译好的包全部拷贝到IDEA工作目录中并打开。

1.2、打开项目配置项

1.3、添加远程连接配置组

2、测试

2.1、在CliDriver类的run方法中随机打上断点

2.2、开启Hive客户端Debug模式

$HIVE_HOME/bin/hive –debug
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2.3、使用debug模式启动本地项目

2.4、在hive客户端执行HQL,切换到IDEA查看

2.5、在Hive Debug模式客户端查看