@Override
  public void load(MapJoinTableContainer[] mapJoinTables,
      MapJoinTableContainerSerDe[] mapJoinTableSerdes)
      throws HiveException {

    Map<Integer, String> parentToInput = desc.getParentToInput();
    Map<Integer, Long> parentKeyCounts = desc.getParentKeyCounts();

    boolean isCrossProduct = false;
    List<ExprNodeDesc> joinExprs = desc.getKeys().values().iterator().next();
    if (joinExprs.size() == 0) {
      isCrossProduct = true;
    }

    boolean useOptimizedTables = HiveConf.getBoolVar(
        hconf, HiveConf.ConfVars.HIVE_MAPJOIN_USE_OPTIMIZED_TABLE);
    boolean useHybridGraceHashJoin = desc.isHybridHashJoin();
    boolean isFirstKey = true;

    // Get the total available memory from memory manager
    long totalMapJoinMemory = desc.getMemoryNeeded();
    LOG.info("Memory manager allocates " + totalMapJoinMemory + " bytes for the loading hashtable.");
    if (totalMapJoinMemory <= 0) {
      totalMapJoinMemory = HiveConf.getLongVar(
        hconf, HiveConf.ConfVars.HIVE_CONVERT_JOIN_NOCONDITIONAL_TASK_THRESHOLD);
    }

    long processMaxMemory = ManagementFactory.getMemoryMXBean().getHeapMemoryUsage().getMax();
    if (totalMapJoinMemory > processMaxMemory) {
      float hashtableMemoryUsage = HiveConf.getFloatVar(
          hconf, HiveConf.ConfVars.HIVE_HASHTABLE_FOLLOWBY_GBY_MAX_MEMORY_USAGE);
      LOG.warn("totalMapJoinMemory value of " + totalMapJoinMemory +
          " is greater than the max memory size of " + processMaxMemory);
      // Don't want to attempt to grab more memory than we have available .. percentage is a bit arbitrary
      totalMapJoinMemory = (long) (processMaxMemory * hashtableMemoryUsage);
    }

    // Only applicable to n-way Hybrid Grace Hash Join
    HybridHashTableConf nwayConf = null;
    long totalSize = 0;
    int biggest = 0;                                // position of the biggest small table
    Map<Integer, Long> tableMemorySizes = null;
    if (useHybridGraceHashJoin && mapJoinTables.length > 2) {
      // Create a Conf for n-way HybridHashTableContainers
      nwayConf = new HybridHashTableConf();
      LOG.info("N-way join: " + (mapJoinTables.length - 1) + " small tables.");

      // Find the biggest small table; also calculate total data size of all small tables
      long maxSize = Long.MIN_VALUE; // the size of the biggest small table
      for (int pos = 0; pos < mapJoinTables.length; pos++) {
        if (pos == desc.getPosBigTable()) {
          continue;
        }
        long smallTableSize = desc.getParentDataSizes().get(pos);
        totalSize += smallTableSize;
        if (maxSize < smallTableSize) {
          maxSize = smallTableSize;
          biggest = pos;
        }
      }

      tableMemorySizes = divideHybridHashTableMemory(mapJoinTables, desc,
          totalSize, totalMapJoinMemory);
      // Using biggest small table, calculate number of partitions to create for each small table
      long memory = tableMemorySizes.get(biggest);
      int numPartitions = 0;
      try {
        numPartitions = HybridHashTableContainer.calcNumPartitions(memory, maxSize,
            HiveConf.getIntVar(hconf, HiveConf.ConfVars.HIVE_HYBRIDGRACE_HASHJOIN_MIN_NUM_PARTITIONS),
            HiveConf.getIntVar(hconf, HiveConf.ConfVars.HIVE_HYBRIDGRACE_HASHJOIN_MIN_WB_SIZE));
      } catch (IOException e) {
        throw new HiveException(e);
      }
      nwayConf.setNumberOfPartitions(numPartitions);
    }
    MemoryMonitorInfo memoryMonitorInfo = desc.getMemoryMonitorInfo();
    boolean doMemCheck = false;
    long effectiveThreshold = 0;
    if (memoryMonitorInfo != null) {
      effectiveThreshold = memoryMonitorInfo.getEffectiveThreshold(desc.getMaxMemoryAvailable());

      // hash table loading happens in server side, LlapDecider could kick out some fragments to run outside of LLAP.
      // Flip the flag at runtime in case if we are running outside of LLAP
      if (!LlapDaemonInfo.INSTANCE.isLlap()) {
        memoryMonitorInfo.setLlap(false);
      }
      if (memoryMonitorInfo.doMemoryMonitoring()) {
        doMemCheck = true;
        LOG.info("Memory monitoring for hash table loader enabled. {}", memoryMonitorInfo);
      }
    }

    if (!doMemCheck) {
      LOG.info("Not doing hash table memory monitoring. {}", memoryMonitorInfo);
    }
    for (int pos = 0; pos < mapJoinTables.length; pos++) {
      if (pos == desc.getPosBigTable()) {
        continue;
      }

      long numEntries = 0;
      String inputName = parentToInput.get(pos);
      LogicalInput input = tezContext.getInput(inputName);

      try {
        input.start();
        tezContext.getTezProcessorContext().waitForAnyInputReady(
            Collections.<Input> singletonList(input));
      } catch (Exception e) {
        throw new HiveException(e);
      }

      try {
        KeyValueReader kvReader = (KeyValueReader) input.getReader();
        MapJoinObjectSerDeContext keyCtx = mapJoinTableSerdes[pos].getKeyContext(),
          valCtx = mapJoinTableSerdes[pos].getValueContext();
        if (useOptimizedTables) {
          ObjectInspector keyOi = keyCtx.getSerDe().getObjectInspector();
          if (!MapJoinBytesTableContainer.isSupportedKey(keyOi)) {
            if (isFirstKey) {
              useOptimizedTables = false;
              LOG.info(describeOi("Not using optimized hash table. " +
                           "Only a subset of mapjoin keys is supported. Unsupported key: ", keyOi));
            } else {
              throw new HiveException(describeOi(
                  "Only a subset of mapjoin keys is supported. Unsupported key: ", keyOi));
            }
          }
        }
        isFirstKey = false;
        Long keyCountObj = parentKeyCounts.get(pos);
        long estKeyCount = (keyCountObj == null) ? -1 : keyCountObj;

        long inputRecords = -1;
        try {
          //TODO : Need to use class instead of string.
          // https://issues.apache.org/jira/browse/HIVE-23981
          inputRecords = ((AbstractLogicalInput) input).getContext().getCounters().
                  findCounter("org.apache.tez.common.counters.TaskCounter",
                          "APPROXIMATE_INPUT_RECORDS").getValue();
        } catch (Exception e) {
          LOG.debug("Failed to get value for counter APPROXIMATE_INPUT_RECORDS", e);
        }
        long keyCount = Math.max(estKeyCount, inputRecords);

        long memory = 0;
        if (useHybridGraceHashJoin) {
          if (mapJoinTables.length > 2) {
            memory = tableMemorySizes.get(pos);
          } else {  // binary join
            memory = totalMapJoinMemory;
          }
        }

        MapJoinTableContainer tableContainer;
        if (useOptimizedTables) {
          if (!useHybridGraceHashJoin || isCrossProduct) {
            tableContainer = new MapJoinBytesTableContainer(hconf, valCtx, keyCount, 0);
          } else {
            tableContainer = new HybridHashTableContainer(hconf, keyCount, memory,
                desc.getParentDataSizes().get(pos), nwayConf);
          }
        } else {
          tableContainer = new HashMapWrapper(hconf, keyCount);
        }

        LOG.info("Loading hash table for input: {} cacheKey: {} tableContainer: {} smallTablePos: {} " +
                        "estKeyCount : {} keyCount : {}", inputName, cacheKey,
                tableContainer.getClass().getSimpleName(), pos, estKeyCount, keyCount);

        tableContainer.setSerde(keyCtx, valCtx);
        long startTime = System.currentTimeMillis();
        while (kvReader.next()) {
          tableContainer.putRow((Writable) kvReader.getCurrentKey(), (Writable) kvReader.getCurrentValue());
          numEntries++;
          if (doMemCheck && (numEntries % memoryMonitorInfo.getMemoryCheckInterval() == 0)) {
            final long estMemUsage = tableContainer.getEstimatedMemorySize();
            if (estMemUsage > effectiveThreshold) {
              String msg = "Hash table loading exceeded memory limits for input: " + inputName +
                " numEntries: " + numEntries + " estimatedMemoryUsage: " + estMemUsage +
                " effectiveThreshold: " + effectiveThreshold + " memoryMonitorInfo: " + memoryMonitorInfo;
              LOG.error(msg);
              throw new MapJoinMemoryExhaustionError(msg);
            } else {
              LOG.info(
                  "Checking hash table loader memory usage for input: {} numEntries: {} "
                      + "estimatedMemoryUsage: {} effectiveThreshold: {}",
                  inputName, numEntries, estMemUsage, effectiveThreshold);
            }
          }
        }
        long delta = System.currentTimeMillis() - startTime;
        htLoadCounter.increment(delta);
        tableContainer.seal();
        mapJoinTables[pos] = tableContainer;
        if (doMemCheck) {
          LOG.info("Finished loading hash table for input: {} cacheKey: {} numEntries: {} " +
                          "estimatedMemoryUsage: {} Load Time : {} ",
            inputName, cacheKey, numEntries, tableContainer.getEstimatedMemorySize(), delta);
        } else {
          LOG.info("Finished loading hash table for input: {} cacheKey: {} numEntries: {} Load Time : {} ",
                  inputName, cacheKey, numEntries, delta);
        }
      } catch (Exception e) {
        throw new HiveException(e);
      }
    }
  }
HashTableLoader for Tez constructs the hashtable from records read from
a broadcast edge.
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/HashTableLoader.java