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From jihoon...@apache.org
Subject [05/16] tajo git commit: TAJO-1288: Refactoring org.apache.tajo.master package.
Date Thu, 08 Jan 2015 16:17:22 GMT
http://git-wip-us.apache.org/repos/asf/tajo/blob/1c29c1cb/tajo-core/src/main/java/org/apache/tajo/querymaster/Repartitioner.java
----------------------------------------------------------------------
diff --git a/tajo-core/src/main/java/org/apache/tajo/querymaster/Repartitioner.java b/tajo-core/src/main/java/org/apache/tajo/querymaster/Repartitioner.java
new file mode 100644
index 0000000..5a35674
--- /dev/null
+++ b/tajo-core/src/main/java/org/apache/tajo/querymaster/Repartitioner.java
@@ -0,0 +1,1250 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.tajo.querymaster;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.collect.Lists;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.fs.Path;
+import org.apache.tajo.ExecutionBlockId;
+import org.apache.tajo.SessionVars;
+import org.apache.tajo.algebra.JoinType;
+import org.apache.tajo.catalog.*;
+import org.apache.tajo.catalog.proto.CatalogProtos.StoreType;
+import org.apache.tajo.catalog.statistics.StatisticsUtil;
+import org.apache.tajo.catalog.statistics.TableStats;
+import org.apache.tajo.conf.TajoConf.ConfVars;
+import org.apache.tajo.engine.planner.PhysicalPlannerImpl;
+import org.apache.tajo.engine.planner.RangePartitionAlgorithm;
+import org.apache.tajo.engine.planner.UniformRangePartition;
+import org.apache.tajo.engine.planner.enforce.Enforcer;
+import org.apache.tajo.engine.planner.global.DataChannel;
+import org.apache.tajo.engine.planner.global.ExecutionBlock;
+import org.apache.tajo.engine.planner.global.GlobalPlanner;
+import org.apache.tajo.engine.planner.global.MasterPlan;
+import org.apache.tajo.engine.utils.TupleUtil;
+import org.apache.tajo.exception.InternalException;
+import org.apache.tajo.ipc.TajoWorkerProtocol.DistinctGroupbyEnforcer.MultipleAggregationStage;
+import org.apache.tajo.ipc.TajoWorkerProtocol.EnforceProperty;
+import org.apache.tajo.querymaster.Task.IntermediateEntry;
+import org.apache.tajo.plan.logical.SortNode.SortPurpose;
+import org.apache.tajo.plan.util.PlannerUtil;
+import org.apache.tajo.plan.PlanningException;
+import org.apache.tajo.plan.logical.*;
+import org.apache.tajo.storage.FileStorageManager;
+import org.apache.tajo.storage.StorageManager;
+import org.apache.tajo.storage.RowStoreUtil;
+import org.apache.tajo.storage.TupleRange;
+import org.apache.tajo.storage.fragment.FileFragment;
+import org.apache.tajo.storage.fragment.Fragment;
+import org.apache.tajo.util.Pair;
+import org.apache.tajo.unit.StorageUnit;
+import org.apache.tajo.util.TUtil;
+import org.apache.tajo.util.TajoIdUtils;
+import org.apache.tajo.worker.FetchImpl;
+
+import java.io.IOException;
+import java.io.UnsupportedEncodingException;
+import java.math.BigInteger;
+import java.net.URI;
+import java.util.*;
+import java.util.Map.Entry;
+
+import static org.apache.tajo.plan.serder.PlanProto.ShuffleType;
+import static org.apache.tajo.plan.serder.PlanProto.ShuffleType.*;
+
+/**
+ * Repartitioner creates non-leaf tasks and shuffles intermediate data.
+ * It supports two repartition methods, such as hash and range repartition.
+ */
+public class Repartitioner {
+  private static final Log LOG = LogFactory.getLog(Repartitioner.class);
+
+  private final static int HTTP_REQUEST_MAXIMUM_LENGTH = 1900;
+  private final static String UNKNOWN_HOST = "unknown";
+
+  public static void scheduleFragmentsForJoinQuery(TaskSchedulerContext schedulerContext, Stage stage)
+      throws IOException {
+    MasterPlan masterPlan = stage.getMasterPlan();
+    ExecutionBlock execBlock = stage.getBlock();
+    QueryMasterTask.QueryMasterTaskContext masterContext = stage.getContext();
+
+    ScanNode[] scans = execBlock.getScanNodes();
+
+    Path tablePath;
+    Fragment[] fragments = new Fragment[scans.length];
+    long[] stats = new long[scans.length];
+
+    // initialize variables from the child operators
+    for (int i = 0; i < scans.length; i++) {
+      TableDesc tableDesc = masterContext.getTableDescMap().get(scans[i].getCanonicalName());
+      if (tableDesc == null) { // if it is a real table stored on storage
+        FileStorageManager storageManager =
+            (FileStorageManager)StorageManager.getFileStorageManager(stage.getContext().getConf());
+
+        tablePath = storageManager.getTablePath(scans[i].getTableName());
+        if (execBlock.getUnionScanMap() != null && !execBlock.getUnionScanMap().isEmpty()) {
+          for (Map.Entry<ExecutionBlockId, ExecutionBlockId> unionScanEntry: execBlock.getUnionScanMap().entrySet()) {
+            ExecutionBlockId originScanEbId = unionScanEntry.getKey();
+            stats[i] += masterContext.getStage(originScanEbId).getResultStats().getNumBytes();
+          }
+        } else {
+          ExecutionBlockId scanEBId = TajoIdUtils.createExecutionBlockId(scans[i].getTableName());
+          stats[i] = masterContext.getStage(scanEBId).getResultStats().getNumBytes();
+        }
+        fragments[i] = new FileFragment(scans[i].getCanonicalName(), tablePath, 0, 0, new String[]{UNKNOWN_HOST});
+      } else {
+        try {
+          stats[i] = GlobalPlanner.computeDescendentVolume(scans[i]);
+        } catch (PlanningException e) {
+          throw new IOException(e);
+        }
+
+        StorageManager storageManager =
+            StorageManager.getStorageManager(stage.getContext().getConf(), tableDesc.getMeta().getStoreType());
+
+        // if table has no data, storageManager will return empty FileFragment.
+        // So, we need to handle FileFragment by its size.
+        // If we don't check its size, it can cause IndexOutOfBoundsException.
+        List<Fragment> fileFragments = storageManager.getSplits(scans[i].getCanonicalName(), tableDesc);
+        if (fileFragments.size() > 0) {
+          fragments[i] = fileFragments.get(0);
+        } else {
+          fragments[i] = new FileFragment(scans[i].getCanonicalName(), new Path(tableDesc.getPath()), 0, 0, new String[]{UNKNOWN_HOST});
+        }
+      }
+    }
+
+    // If one of inner join tables has no input data, it means that this execution block has no result row.
+    JoinNode joinNode = PlannerUtil.findMostBottomNode(execBlock.getPlan(), NodeType.JOIN);
+    if (joinNode != null) {
+      if ( (joinNode.getJoinType() == JoinType.INNER)) {
+        LogicalNode leftNode = joinNode.getLeftChild();
+        LogicalNode rightNode = joinNode.getRightChild();
+        for (int i = 0; i < stats.length; i++) {
+          if (scans[i].getPID() == leftNode.getPID() || scans[i].getPID() == rightNode.getPID()) {
+            if (stats[i] == 0) {
+              LOG.info(scans[i] + " 's input data is zero. Inner join's result is empty.");
+              return;
+            }
+          }
+        }
+      }
+    }
+
+    // If node is outer join and a preserved relation is empty, it should return zero rows.
+    joinNode = PlannerUtil.findTopNode(execBlock.getPlan(), NodeType.JOIN);
+    if (joinNode != null) {
+      // If all stats are zero, return
+      boolean isEmptyAllJoinTables = true;
+      for (int i = 0; i < stats.length; i++) {
+        if (stats[i] > 0) {
+          isEmptyAllJoinTables = false;
+          break;
+        }
+      }
+      if (isEmptyAllJoinTables) {
+        LOG.info("All input join tables are empty.");
+        return;
+      }
+
+      // find left top scan node
+      ScanNode leftScanNode = PlannerUtil.findTopNode(joinNode.getLeftChild(), NodeType.SCAN);
+      ScanNode rightScanNode = PlannerUtil.findTopNode(joinNode.getRightChild(), NodeType.SCAN);
+
+      long leftStats = -1;
+      long rightStats = -1;
+      if (stats.length == 2) {
+        for (int i = 0; i < stats.length; i++) {
+          if (scans[i].equals(leftScanNode)) {
+            leftStats = stats[i];
+          } else if (scans[i].equals(rightScanNode)) {
+            rightStats = stats[i];
+          }
+        }
+        if (joinNode.getJoinType() == JoinType.LEFT_OUTER) {
+          if (leftStats == 0) {
+            return;
+          }
+        }
+        if (joinNode.getJoinType() == JoinType.RIGHT_OUTER) {
+          if (rightStats == 0) {
+            return;
+          }
+        }
+      }
+    }
+
+    // Assigning either fragments or fetch urls to query units
+    boolean isAllBroadcastTable = true;
+    for (int i = 0; i < scans.length; i++) {
+      if (!execBlock.isBroadcastTable(scans[i].getCanonicalName())) {
+        isAllBroadcastTable = false;
+        break;
+      }
+    }
+
+
+    if (isAllBroadcastTable) { // if all relations of this EB are broadcasted
+      // set largest table to normal mode
+      long maxStats = Long.MIN_VALUE;
+      int maxStatsScanIdx = -1;
+      for (int i = 0; i < scans.length; i++) {
+        // finding largest table.
+        // If stats == 0, can't be base table.
+        if (stats[i] > 0 && stats[i] > maxStats) {
+          maxStats = stats[i];
+          maxStatsScanIdx = i;
+        }
+      }
+      if (maxStatsScanIdx == -1) {
+        maxStatsScanIdx = 0;
+      }
+      int baseScanIdx = maxStatsScanIdx;
+      scans[baseScanIdx].setBroadcastTable(false);
+      execBlock.removeBroadcastTable(scans[baseScanIdx].getCanonicalName());
+      LOG.info(String.format("[Distributed Join Strategy] : Broadcast Join with all tables, base_table=%s, base_volume=%d",
+          scans[baseScanIdx].getCanonicalName(), stats[baseScanIdx]));
+      scheduleLeafTasksWithBroadcastTable(schedulerContext, stage, baseScanIdx, fragments);
+    } else if (!execBlock.getBroadcastTables().isEmpty()) { // If some relations of this EB are broadcasted
+      boolean hasNonLeafNode = false;
+      List<Integer> largeScanIndexList = new ArrayList<Integer>();
+      List<Integer> broadcastIndexList = new ArrayList<Integer>();
+      String nonLeafScanNames = "";
+      String namePrefix = "";
+      long maxStats = Long.MIN_VALUE;
+      int maxStatsScanIdx = -1;
+      for (int i = 0; i < scans.length; i++) {
+        if (scans[i].getTableDesc().getMeta().getStoreType() == StoreType.RAW) {
+          // Intermediate data scan
+          hasNonLeafNode = true;
+          largeScanIndexList.add(i);
+          nonLeafScanNames += namePrefix + scans[i].getCanonicalName();
+          namePrefix = ",";
+        }
+        if (execBlock.isBroadcastTable(scans[i].getCanonicalName())) {
+          broadcastIndexList.add(i);
+        } else {
+          // finding largest table.
+          if (stats[i] > 0 && stats[i] > maxStats) {
+            maxStats = stats[i];
+            maxStatsScanIdx = i;
+          }
+        }
+      }
+      if (maxStatsScanIdx == -1) {
+        maxStatsScanIdx = 0;
+      }
+
+      if (!hasNonLeafNode) {
+        if (largeScanIndexList.size() > 1) {
+          String largeTableNames = "";
+          for (Integer eachId : largeScanIndexList) {
+            largeTableNames += scans[eachId].getTableName() + ",";
+          }
+          throw new IOException("Broadcast join with leaf node should have only one large table, " +
+              "but " + largeScanIndexList.size() + ", tables=" + largeTableNames);
+        }
+        int baseScanIdx = largeScanIndexList.isEmpty() ? maxStatsScanIdx : largeScanIndexList.get(0);
+        LOG.info(String.format("[Distributed Join Strategy] : Broadcast Join, base_table=%s, base_volume=%d",
+            scans[baseScanIdx].getCanonicalName(), stats[baseScanIdx]));
+        scheduleLeafTasksWithBroadcastTable(schedulerContext, stage, baseScanIdx, fragments);
+      } else {
+        if (largeScanIndexList.size() > 2) {
+          throw new IOException("Symmetric Repartition Join should have two scan node, but " + nonLeafScanNames);
+        }
+
+        //select intermediate scan and stats
+        ScanNode[] intermediateScans = new ScanNode[largeScanIndexList.size()];
+        long[] intermediateScanStats = new long[largeScanIndexList.size()];
+        Fragment[] intermediateFragments = new Fragment[largeScanIndexList.size()];
+        int index = 0;
+        for (Integer eachIdx : largeScanIndexList) {
+          intermediateScans[index] = scans[eachIdx];
+          intermediateScanStats[index] = stats[eachIdx];
+          intermediateFragments[index++] = fragments[eachIdx];
+        }
+        Fragment[] broadcastFragments = new Fragment[broadcastIndexList.size()];
+        ScanNode[] broadcastScans = new ScanNode[broadcastIndexList.size()];
+        index = 0;
+        for (Integer eachIdx : broadcastIndexList) {
+          scans[eachIdx].setBroadcastTable(true);
+          broadcastScans[index] = scans[eachIdx];
+          broadcastFragments[index] = fragments[eachIdx];
+          index++;
+        }
+        LOG.info(String.format("[Distributed Join Strategy] : Broadcast Join, join_node=%s", nonLeafScanNames));
+        scheduleSymmetricRepartitionJoin(masterContext, schedulerContext, stage,
+            intermediateScans, intermediateScanStats, intermediateFragments, broadcastScans, broadcastFragments);
+      }
+    } else {
+      LOG.info("[Distributed Join Strategy] : Symmetric Repartition Join");
+      scheduleSymmetricRepartitionJoin(masterContext, schedulerContext, stage, scans, stats, fragments, null, null);
+    }
+  }
+
+  /**
+   * Scheduling in tech case of Symmetric Repartition Join
+   * @param masterContext
+   * @param schedulerContext
+   * @param stage
+   * @param scans
+   * @param stats
+   * @param fragments
+   * @throws IOException
+   */
+  private static void scheduleSymmetricRepartitionJoin(QueryMasterTask.QueryMasterTaskContext masterContext,
+                                                       TaskSchedulerContext schedulerContext,
+                                                       Stage stage,
+                                                       ScanNode[] scans,
+                                                       long[] stats,
+                                                       Fragment[] fragments,
+                                                       ScanNode[] broadcastScans,
+                                                       Fragment[] broadcastFragments) throws IOException {
+    MasterPlan masterPlan = stage.getMasterPlan();
+    ExecutionBlock execBlock = stage.getBlock();
+    // The hash map is modeling as follows:
+    // <Part Id, <EbId, List<Intermediate Data>>>
+    Map<Integer, Map<ExecutionBlockId, List<IntermediateEntry>>> hashEntries =
+        new HashMap<Integer, Map<ExecutionBlockId, List<IntermediateEntry>>>();
+
+    // Grouping IntermediateData by a partition key and a table name
+    List<ExecutionBlock> childBlocks = masterPlan.getChilds(stage.getId());
+
+    // In the case of join with union, there is one ScanNode for union.
+    Map<ExecutionBlockId, ExecutionBlockId> unionScanMap = execBlock.getUnionScanMap();
+    for (ExecutionBlock childBlock : childBlocks) {
+      ExecutionBlockId scanEbId = unionScanMap.get(childBlock.getId());
+      if (scanEbId == null) {
+        scanEbId = childBlock.getId();
+      }
+      Stage childExecSM = stage.getContext().getStage(childBlock.getId());
+
+      if (childExecSM.getHashShuffleIntermediateEntries() != null &&
+          !childExecSM.getHashShuffleIntermediateEntries().isEmpty()) {
+        for (IntermediateEntry intermediateEntry: childExecSM.getHashShuffleIntermediateEntries()) {
+          intermediateEntry.setEbId(childBlock.getId());
+          if (hashEntries.containsKey(intermediateEntry.getPartId())) {
+            Map<ExecutionBlockId, List<IntermediateEntry>> tbNameToInterm =
+                hashEntries.get(intermediateEntry.getPartId());
+
+            if (tbNameToInterm.containsKey(scanEbId)) {
+              tbNameToInterm.get(scanEbId).add(intermediateEntry);
+            } else {
+              tbNameToInterm.put(scanEbId, TUtil.newList(intermediateEntry));
+            }
+          } else {
+            Map<ExecutionBlockId, List<IntermediateEntry>> tbNameToInterm =
+                new HashMap<ExecutionBlockId, List<IntermediateEntry>>();
+            tbNameToInterm.put(scanEbId, TUtil.newList(intermediateEntry));
+            hashEntries.put(intermediateEntry.getPartId(), tbNameToInterm);
+          }
+        }
+      } else {
+        //if no intermidatedata(empty table), make empty entry
+        int emptyPartitionId = 0;
+        if (hashEntries.containsKey(emptyPartitionId)) {
+          Map<ExecutionBlockId, List<IntermediateEntry>> tbNameToInterm = hashEntries.get(emptyPartitionId);
+          if (tbNameToInterm.containsKey(scanEbId))
+            tbNameToInterm.get(scanEbId).addAll(new ArrayList<IntermediateEntry>());
+          else
+            tbNameToInterm.put(scanEbId, new ArrayList<IntermediateEntry>());
+        } else {
+          Map<ExecutionBlockId, List<IntermediateEntry>> tbNameToInterm =
+              new HashMap<ExecutionBlockId, List<IntermediateEntry>>();
+          tbNameToInterm.put(scanEbId, new ArrayList<IntermediateEntry>());
+          hashEntries.put(emptyPartitionId, tbNameToInterm);
+        }
+      }
+    }
+
+    // hashEntries can be zero if there are no input data.
+    // In the case, it will cause the zero divided exception.
+    // it avoids this problem.
+    int[] avgSize = new int[2];
+    avgSize[0] = hashEntries.size() == 0 ? 0 : (int) (stats[0] / hashEntries.size());
+    avgSize[1] = hashEntries.size() == 0 ? 0 : (int) (stats[1] / hashEntries.size());
+    int bothFetchSize = avgSize[0] + avgSize[1];
+
+    // Getting the desire number of join tasks according to the volumn
+    // of a larger table
+    int largerIdx = stats[0] >= stats[1] ? 0 : 1;
+    int desireJoinTaskVolumn = stage.getMasterPlan().getContext().getInt(SessionVars.JOIN_TASK_INPUT_SIZE);
+
+    // calculate the number of tasks according to the data size
+    int mb = (int) Math.ceil((double) stats[largerIdx] / 1048576);
+    LOG.info("Larger intermediate data is approximately " + mb + " MB");
+    // determine the number of task per 64MB
+    int maxTaskNum = (int) Math.ceil((double) mb / desireJoinTaskVolumn);
+    LOG.info("The calculated number of tasks is " + maxTaskNum);
+    LOG.info("The number of total shuffle keys is " + hashEntries.size());
+    // the number of join tasks cannot be larger than the number of
+    // distinct partition ids.
+    int joinTaskNum = Math.min(maxTaskNum, hashEntries.size());
+    LOG.info("The determined number of join tasks is " + joinTaskNum);
+
+    List<Fragment> rightFragments = new ArrayList<Fragment>();
+    rightFragments.add(fragments[1]);
+
+    if (broadcastFragments != null) {
+      //In this phase a ScanNode has a single fragment.
+      //If there are more than one data files, that files should be added to fragments or partition path
+      for (ScanNode eachScan: broadcastScans) {
+        Path[] partitionScanPaths = null;
+        TableDesc tableDesc = masterContext.getTableDescMap().get(eachScan.getCanonicalName());
+        if (eachScan.getType() == NodeType.PARTITIONS_SCAN) {
+          FileStorageManager storageManager =
+              (FileStorageManager)StorageManager.getFileStorageManager(stage.getContext().getConf());
+
+          PartitionedTableScanNode partitionScan = (PartitionedTableScanNode)eachScan;
+          partitionScanPaths = partitionScan.getInputPaths();
+          // set null to inputPaths in getFragmentsFromPartitionedTable()
+          getFragmentsFromPartitionedTable(storageManager, eachScan, tableDesc);
+          partitionScan.setInputPaths(partitionScanPaths);
+        } else {
+          StorageManager storageManager = StorageManager.getStorageManager(stage.getContext().getConf(),
+              tableDesc.getMeta().getStoreType());
+          Collection<Fragment> scanFragments = storageManager.getSplits(eachScan.getCanonicalName(),
+              tableDesc, eachScan);
+          if (scanFragments != null) {
+            rightFragments.addAll(scanFragments);
+          }
+        }
+      }
+    }
+    Stage.scheduleFragment(stage, fragments[0], rightFragments);
+
+    // Assign partitions to tasks in a round robin manner.
+    for (Entry<Integer, Map<ExecutionBlockId, List<IntermediateEntry>>> entry
+        : hashEntries.entrySet()) {
+      addJoinShuffle(stage, entry.getKey(), entry.getValue());
+    }
+
+    schedulerContext.setTaskSize((int) Math.ceil((double) bothFetchSize / joinTaskNum));
+    schedulerContext.setEstimatedTaskNum(joinTaskNum);
+  }
+
+  /**
+   * merge intermediate entry by ebid, pullhost
+   * @param hashEntries
+   * @return
+   */
+  public static Map<Integer, Map<ExecutionBlockId, List<IntermediateEntry>>> mergeIntermediateByPullHost(
+      Map<Integer, Map<ExecutionBlockId, List<IntermediateEntry>>> hashEntries) {
+    Map<Integer, Map<ExecutionBlockId, List<IntermediateEntry>>> mergedHashEntries =
+        new HashMap<Integer, Map<ExecutionBlockId, List<IntermediateEntry>>>();
+
+    for(Entry<Integer, Map<ExecutionBlockId, List<IntermediateEntry>>> entry: hashEntries.entrySet()) {
+      Integer partId = entry.getKey();
+      for (Entry<ExecutionBlockId, List<IntermediateEntry>> partEntry: entry.getValue().entrySet()) {
+        List<IntermediateEntry> intermediateList = partEntry.getValue();
+        if (intermediateList == null || intermediateList.isEmpty()) {
+          continue;
+        }
+        ExecutionBlockId ebId = partEntry.getKey();
+        // EBID + PullHost -> IntermediateEntry
+        // In the case of union partEntry.getKey() return's delegated EBID.
+        // Intermediate entries are merged by real EBID.
+        Map<String, IntermediateEntry> ebMerged = new HashMap<String, IntermediateEntry>();
+
+        for (IntermediateEntry eachIntermediate: intermediateList) {
+          String ebMergedKey = eachIntermediate.getEbId().toString() + eachIntermediate.getPullHost().getPullAddress();
+          IntermediateEntry intermediateEntryPerPullHost = ebMerged.get(ebMergedKey);
+          if (intermediateEntryPerPullHost == null) {
+            intermediateEntryPerPullHost = new IntermediateEntry(-1, -1, partId, eachIntermediate.getPullHost());
+            intermediateEntryPerPullHost.setEbId(eachIntermediate.getEbId());
+            ebMerged.put(ebMergedKey, intermediateEntryPerPullHost);
+          }
+          intermediateEntryPerPullHost.setVolume(intermediateEntryPerPullHost.getVolume() + eachIntermediate.getVolume());
+        }
+
+        List<IntermediateEntry> ebIntermediateEntries = new ArrayList<IntermediateEntry>(ebMerged.values());
+
+        Map<ExecutionBlockId, List<IntermediateEntry>> mergedPartEntries = mergedHashEntries.get(partId);
+        if (mergedPartEntries == null) {
+          mergedPartEntries = new HashMap<ExecutionBlockId, List<IntermediateEntry>>();
+          mergedHashEntries.put(partId, mergedPartEntries);
+        }
+        mergedPartEntries.put(ebId, ebIntermediateEntries);
+      }
+    }
+    return mergedHashEntries;
+  }
+
+  /**
+   * It creates a number of fragments for all partitions.
+   */
+  public static List<Fragment> getFragmentsFromPartitionedTable(FileStorageManager sm,
+                                                                          ScanNode scan,
+                                                                          TableDesc table) throws IOException {
+    List<Fragment> fragments = Lists.newArrayList();
+    PartitionedTableScanNode partitionsScan = (PartitionedTableScanNode) scan;
+    fragments.addAll(sm.getSplits(
+        scan.getCanonicalName(), table.getMeta(), table.getSchema(), partitionsScan.getInputPaths()));
+    partitionsScan.setInputPaths(null);
+    return fragments;
+  }
+
+  private static void scheduleLeafTasksWithBroadcastTable(TaskSchedulerContext schedulerContext, Stage stage,
+                                                          int baseScanId, Fragment[] fragments) throws IOException {
+    ExecutionBlock execBlock = stage.getBlock();
+    ScanNode[] scans = execBlock.getScanNodes();
+
+    for (int i = 0; i < scans.length; i++) {
+      if (i != baseScanId) {
+        scans[i].setBroadcastTable(true);
+      }
+    }
+
+    // Large table(baseScan)
+    //  -> add all fragment to baseFragments
+    //  -> each fragment is assigned to a Task by DefaultTaskScheduler.handle()
+    // Broadcast table
+    //  all fragments or paths assigned every Large table's scan task.
+    //  -> PARTITIONS_SCAN
+    //     . add all partition paths to node's inputPaths variable
+    //  -> SCAN
+    //     . add all fragments to broadcastFragments
+    Collection<Fragment> baseFragments = null;
+    List<Fragment> broadcastFragments = new ArrayList<Fragment>();
+    for (int i = 0; i < scans.length; i++) {
+      ScanNode scan = scans[i];
+      TableDesc desc = stage.getContext().getTableDescMap().get(scan.getCanonicalName());
+      TableMeta meta = desc.getMeta();
+
+      Collection<Fragment> scanFragments;
+      Path[] partitionScanPaths = null;
+      if (scan.getType() == NodeType.PARTITIONS_SCAN) {
+        PartitionedTableScanNode partitionScan = (PartitionedTableScanNode)scan;
+        partitionScanPaths = partitionScan.getInputPaths();
+        // set null to inputPaths in getFragmentsFromPartitionedTable()
+        FileStorageManager storageManager =
+            (FileStorageManager)StorageManager.getFileStorageManager(stage.getContext().getConf());
+        scanFragments = getFragmentsFromPartitionedTable(storageManager, scan, desc);
+      } else {
+        StorageManager storageManager =
+            StorageManager.getStorageManager(stage.getContext().getConf(), desc.getMeta().getStoreType());
+
+        scanFragments = storageManager.getSplits(scan.getCanonicalName(), desc, scan);
+      }
+
+      if (scanFragments != null) {
+        if (i == baseScanId) {
+          baseFragments = scanFragments;
+        } else {
+          if (scan.getType() == NodeType.PARTITIONS_SCAN) {
+            PartitionedTableScanNode partitionScan = (PartitionedTableScanNode)scan;
+            // PhisicalPlanner make PartitionMergeScanExec when table is boradcast table and inputpaths is not empty
+            partitionScan.setInputPaths(partitionScanPaths);
+          } else {
+            broadcastFragments.addAll(scanFragments);
+          }
+        }
+      }
+    }
+
+    if (baseFragments == null) {
+      throw new IOException("No fragments for " + scans[baseScanId].getTableName());
+    }
+
+    Stage.scheduleFragments(stage, baseFragments, broadcastFragments);
+    schedulerContext.setEstimatedTaskNum(baseFragments.size());
+  }
+
+  private static void addJoinShuffle(Stage stage, int partitionId,
+                                     Map<ExecutionBlockId, List<IntermediateEntry>> grouppedPartitions) {
+    Map<String, List<FetchImpl>> fetches = new HashMap<String, List<FetchImpl>>();
+    for (ExecutionBlock execBlock : stage.getMasterPlan().getChilds(stage.getId())) {
+      if (grouppedPartitions.containsKey(execBlock.getId())) {
+        Collection<FetchImpl> requests = mergeShuffleRequest(partitionId, HASH_SHUFFLE,
+            grouppedPartitions.get(execBlock.getId()));
+        fetches.put(execBlock.getId().toString(), Lists.newArrayList(requests));
+      }
+    }
+
+    if (fetches.isEmpty()) {
+      LOG.info(stage.getId() + "'s " + partitionId + " partition has empty result.");
+      return;
+    }
+    Stage.scheduleFetches(stage, fetches);
+  }
+
+  /**
+   * This method merges the partition request associated with the pullserver's address.
+   * It reduces the number of TCP connections.
+   *
+   * @return key: pullserver's address, value: a list of requests
+   */
+  private static Collection<FetchImpl> mergeShuffleRequest(int partitionId,
+                                                          ShuffleType type,
+                                                          List<IntermediateEntry> partitions) {
+    // ebId + pullhost -> FetchImmpl
+    Map<String, FetchImpl> mergedPartitions = new HashMap<String, FetchImpl>();
+
+    for (IntermediateEntry partition : partitions) {
+      String mergedKey = partition.getEbId().toString() + "," + partition.getPullHost();
+
+      if (mergedPartitions.containsKey(mergedKey)) {
+        FetchImpl fetch = mergedPartitions.get(mergedKey);
+        fetch.addPart(partition.getTaskId(), partition.getAttemptId());
+      } else {
+        // In some cases like union each IntermediateEntry has different EBID.
+        FetchImpl fetch = new FetchImpl(partition.getPullHost(), type, partition.getEbId(), partitionId);
+        fetch.addPart(partition.getTaskId(), partition.getAttemptId());
+        mergedPartitions.put(mergedKey, fetch);
+      }
+    }
+    return mergedPartitions.values();
+  }
+
+  public static void scheduleFragmentsForNonLeafTasks(TaskSchedulerContext schedulerContext,
+                                                      MasterPlan masterPlan, Stage stage, int maxNum)
+      throws IOException {
+    DataChannel channel = masterPlan.getIncomingChannels(stage.getBlock().getId()).get(0);
+    if (channel.getShuffleType() == HASH_SHUFFLE
+        || channel.getShuffleType() == SCATTERED_HASH_SHUFFLE) {
+      scheduleHashShuffledFetches(schedulerContext, masterPlan, stage, channel, maxNum);
+    } else if (channel.getShuffleType() == RANGE_SHUFFLE) {
+      scheduleRangeShuffledFetches(schedulerContext, masterPlan, stage, channel, maxNum);
+    } else {
+      throw new InternalException("Cannot support partition type");
+    }
+  }
+
+  private static TableStats computeChildBlocksStats(QueryMasterTask.QueryMasterTaskContext context, MasterPlan masterPlan,
+                                                    ExecutionBlockId parentBlockId) {
+    List<TableStats> tableStatses = new ArrayList<TableStats>();
+    List<ExecutionBlock> childBlocks = masterPlan.getChilds(parentBlockId);
+    for (ExecutionBlock childBlock : childBlocks) {
+      Stage childStage = context.getStage(childBlock.getId());
+      tableStatses.add(childStage.getResultStats());
+    }
+    return StatisticsUtil.aggregateTableStat(tableStatses);
+  }
+
+  public static void scheduleRangeShuffledFetches(TaskSchedulerContext schedulerContext, MasterPlan masterPlan,
+                                                  Stage stage, DataChannel channel, int maxNum)
+      throws IOException {
+    ExecutionBlock execBlock = stage.getBlock();
+    ScanNode scan = execBlock.getScanNodes()[0];
+    Path tablePath;
+    tablePath = ((FileStorageManager)StorageManager.getFileStorageManager(stage.getContext().getConf()))
+        .getTablePath(scan.getTableName());
+
+    ExecutionBlock sampleChildBlock = masterPlan.getChild(stage.getId(), 0);
+    SortNode sortNode = PlannerUtil.findTopNode(sampleChildBlock.getPlan(), NodeType.SORT);
+    SortSpec [] sortSpecs = sortNode.getSortKeys();
+    Schema sortSchema = new Schema(channel.getShuffleKeys());
+
+    TupleRange[] ranges;
+    int determinedTaskNum;
+
+    // calculate the number of maximum query ranges
+    TableStats totalStat = computeChildBlocksStats(stage.getContext(), masterPlan, stage.getId());
+
+    // If there is an empty table in inner join, it should return zero rows.
+    if (totalStat.getNumBytes() == 0 && totalStat.getColumnStats().size() == 0) {
+      return;
+    }
+    TupleRange mergedRange = TupleUtil.columnStatToRange(sortSpecs, sortSchema, totalStat.getColumnStats(), false);
+
+    if (sortNode.getSortPurpose() == SortPurpose.STORAGE_SPECIFIED) {
+      StoreType storeType = PlannerUtil.getStoreType(masterPlan.getLogicalPlan());
+      CatalogService catalog = stage.getContext().getQueryMasterContext().getWorkerContext().getCatalog();
+      LogicalRootNode rootNode = masterPlan.getLogicalPlan().getRootBlock().getRoot();
+      TableDesc tableDesc = PlannerUtil.getTableDesc(catalog, rootNode.getChild());
+      if (tableDesc == null) {
+        throw new IOException("Can't get table meta data from catalog: " +
+            PlannerUtil.getStoreTableName(masterPlan.getLogicalPlan()));
+      }
+      ranges = StorageManager.getStorageManager(stage.getContext().getConf(), storeType)
+          .getInsertSortRanges(stage.getContext().getQueryContext(), tableDesc,
+              sortNode.getInSchema(), sortSpecs,
+              mergedRange);
+      determinedTaskNum = ranges.length;
+    } else {
+      RangePartitionAlgorithm partitioner = new UniformRangePartition(mergedRange, sortSpecs);
+      BigInteger card = partitioner.getTotalCardinality();
+
+      // if the number of the range cardinality is less than the desired number of tasks,
+      // we set the the number of tasks to the number of range cardinality.
+      if (card.compareTo(BigInteger.valueOf(maxNum)) < 0) {
+        LOG.info(stage.getId() + ", The range cardinality (" + card
+            + ") is less then the desired number of tasks (" + maxNum + ")");
+        determinedTaskNum = card.intValue();
+      } else {
+        determinedTaskNum = maxNum;
+      }
+
+      LOG.info(stage.getId() + ", Try to divide " + mergedRange + " into " + determinedTaskNum +
+          " sub ranges (total units: " + determinedTaskNum + ")");
+      ranges = partitioner.partition(determinedTaskNum);
+      if (ranges == null || ranges.length == 0) {
+        LOG.warn(stage.getId() + " no range infos.");
+      }
+      TupleUtil.setMaxRangeIfNull(sortSpecs, sortSchema, totalStat.getColumnStats(), ranges);
+      if (LOG.isDebugEnabled()) {
+        if (ranges != null) {
+          for (TupleRange eachRange : ranges) {
+            LOG.debug(stage.getId() + " range: " + eachRange.getStart() + " ~ " + eachRange.getEnd());
+          }
+        }
+      }
+    }
+
+    FileFragment dummyFragment = new FileFragment(scan.getTableName(), tablePath, 0, 0, new String[]{UNKNOWN_HOST});
+    Stage.scheduleFragment(stage, dummyFragment);
+
+    List<FetchImpl> fetches = new ArrayList<FetchImpl>();
+    List<ExecutionBlock> childBlocks = masterPlan.getChilds(stage.getId());
+    for (ExecutionBlock childBlock : childBlocks) {
+      Stage childExecSM = stage.getContext().getStage(childBlock.getId());
+      for (Task qu : childExecSM.getTasks()) {
+        for (IntermediateEntry p : qu.getIntermediateData()) {
+          FetchImpl fetch = new FetchImpl(p.getPullHost(), RANGE_SHUFFLE, childBlock.getId(), 0);
+          fetch.addPart(p.getTaskId(), p.getAttemptId());
+          fetches.add(fetch);
+        }
+      }
+    }
+
+    boolean ascendingFirstKey = sortSpecs[0].isAscending();
+    SortedMap<TupleRange, Collection<FetchImpl>> map;
+    if (ascendingFirstKey) {
+      map = new TreeMap<TupleRange, Collection<FetchImpl>>();
+    } else {
+      map = new TreeMap<TupleRange, Collection<FetchImpl>>(new TupleRange.DescendingTupleRangeComparator());
+    }
+
+    Set<FetchImpl> fetchSet;
+    try {
+      RowStoreUtil.RowStoreEncoder encoder = RowStoreUtil.createEncoder(sortSchema);
+      for (int i = 0; i < ranges.length; i++) {
+        fetchSet = new HashSet<FetchImpl>();
+        for (FetchImpl fetch: fetches) {
+          String rangeParam =
+              TupleUtil.rangeToQuery(ranges[i], ascendingFirstKey ? i == (ranges.length - 1) : i == 0, encoder);
+          FetchImpl copy = null;
+          try {
+            copy = fetch.clone();
+          } catch (CloneNotSupportedException e) {
+            throw new RuntimeException(e);
+          }
+          copy.setRangeParams(rangeParam);
+          fetchSet.add(copy);
+        }
+        map.put(ranges[i], fetchSet);
+      }
+
+    } catch (UnsupportedEncodingException e) {
+      LOG.error(e);
+    }
+
+    scheduleFetchesByRoundRobin(stage, map, scan.getTableName(), determinedTaskNum);
+
+    schedulerContext.setEstimatedTaskNum(determinedTaskNum);
+  }
+
+  public static void scheduleFetchesByRoundRobin(Stage stage, Map<?, Collection<FetchImpl>> partitions,
+                                                   String tableName, int num) {
+    int i;
+    Map<String, List<FetchImpl>>[] fetchesArray = new Map[num];
+    for (i = 0; i < num; i++) {
+      fetchesArray[i] = new HashMap<String, List<FetchImpl>>();
+    }
+    i = 0;
+    for (Entry<?, Collection<FetchImpl>> entry : partitions.entrySet()) {
+      Collection<FetchImpl> value = entry.getValue();
+      TUtil.putCollectionToNestedList(fetchesArray[i++], tableName, value);
+      if (i == num) i = 0;
+    }
+    for (Map<String, List<FetchImpl>> eachFetches : fetchesArray) {
+      Stage.scheduleFetches(stage, eachFetches);
+    }
+  }
+
+  @VisibleForTesting
+  public static class FetchGroupMeta {
+    long totalVolume;
+    List<FetchImpl> fetchUrls;
+
+    public FetchGroupMeta(long volume, FetchImpl fetchUrls) {
+      this.totalVolume = volume;
+      this.fetchUrls = Lists.newArrayList(fetchUrls);
+    }
+
+    public FetchGroupMeta addFetche(FetchImpl fetches) {
+      this.fetchUrls.add(fetches);
+      return this;
+    }
+
+    public void increaseVolume(long volume) {
+      this.totalVolume += volume;
+    }
+
+    public long getVolume() {
+      return totalVolume;
+    }
+
+  }
+
+  public static void scheduleHashShuffledFetches(TaskSchedulerContext schedulerContext, MasterPlan masterPlan,
+                                                 Stage stage, DataChannel channel,
+                                                 int maxNum) throws IOException {
+    ExecutionBlock execBlock = stage.getBlock();
+    ScanNode scan = execBlock.getScanNodes()[0];
+    Path tablePath;
+    tablePath = ((FileStorageManager)StorageManager.getFileStorageManager(stage.getContext().getConf()))
+        .getTablePath(scan.getTableName());
+
+    Fragment frag = new FileFragment(scan.getCanonicalName(), tablePath, 0, 0, new String[]{UNKNOWN_HOST});
+    List<Fragment> fragments = new ArrayList<Fragment>();
+    fragments.add(frag);
+    Stage.scheduleFragments(stage, fragments);
+
+    Map<Integer, FetchGroupMeta> finalFetches = new HashMap<Integer, FetchGroupMeta>();
+    Map<ExecutionBlockId, List<IntermediateEntry>> intermediates = new HashMap<ExecutionBlockId,
+        List<IntermediateEntry>>();
+
+    for (ExecutionBlock block : masterPlan.getChilds(execBlock)) {
+      List<IntermediateEntry> partitions = new ArrayList<IntermediateEntry>();
+      partitions.addAll(stage.getContext().getStage(block.getId()).getHashShuffleIntermediateEntries());
+
+      // In scattered hash shuffle, Collecting each IntermediateEntry
+      if (channel.getShuffleType() == SCATTERED_HASH_SHUFFLE) {
+        if (intermediates.containsKey(block.getId())) {
+          intermediates.get(block.getId()).addAll(partitions);
+        } else {
+          intermediates.put(block.getId(), partitions);
+        }
+      }
+
+      // make FetchImpl per PullServer, PartId
+      Map<Integer, List<IntermediateEntry>> hashed = hashByKey(partitions);
+      for (Entry<Integer, List<IntermediateEntry>> interm : hashed.entrySet()) {
+        Map<Task.PullHost, List<IntermediateEntry>> hashedByHost = hashByHost(interm.getValue());
+        for (Entry<Task.PullHost, List<IntermediateEntry>> e : hashedByHost.entrySet()) {
+
+          FetchImpl fetch = new FetchImpl(e.getKey(), channel.getShuffleType(),
+              block.getId(), interm.getKey(), e.getValue());
+
+          long volumeSum = 0;
+          for (IntermediateEntry ie : e.getValue()) {
+            volumeSum += ie.getVolume();
+          }
+
+          if (finalFetches.containsKey(interm.getKey())) {
+            finalFetches.get(interm.getKey()).addFetche(fetch).increaseVolume(volumeSum);
+          } else {
+            finalFetches.put(interm.getKey(), new FetchGroupMeta(volumeSum, fetch));
+          }
+        }
+      }
+    }
+
+    int groupingColumns = 0;
+    LogicalNode[] groupbyNodes = PlannerUtil.findAllNodes(stage.getBlock().getPlan(),
+        new NodeType[]{NodeType.GROUP_BY, NodeType.DISTINCT_GROUP_BY});
+    if (groupbyNodes != null && groupbyNodes.length > 0) {
+      LogicalNode bottomNode = groupbyNodes[0];
+      if (bottomNode.getType() == NodeType.GROUP_BY) {
+        groupingColumns = ((GroupbyNode)bottomNode).getGroupingColumns().length;
+      } else if (bottomNode.getType() == NodeType.DISTINCT_GROUP_BY) {
+        DistinctGroupbyNode distinctNode = PlannerUtil.findMostBottomNode(stage.getBlock().getPlan(), NodeType.DISTINCT_GROUP_BY);
+        if (distinctNode == null) {
+          LOG.warn(stage.getId() + ", Can't find current DistinctGroupbyNode");
+          distinctNode = (DistinctGroupbyNode)bottomNode;
+        }
+        groupingColumns = distinctNode.getGroupingColumns().length;
+
+        Enforcer enforcer = execBlock.getEnforcer();
+        EnforceProperty property = PhysicalPlannerImpl.getAlgorithmEnforceProperty(enforcer, distinctNode);
+        if (property != null) {
+          if (property.getDistinct().getIsMultipleAggregation()) {
+            MultipleAggregationStage mulAggStage = property.getDistinct().getMultipleAggregationStage();
+            if (mulAggStage != MultipleAggregationStage.THRID_STAGE) {
+              groupingColumns = distinctNode.getOutSchema().size();
+            }
+          }
+        }
+      }
+    }
+    // get a proper number of tasks
+    int determinedTaskNum = Math.min(maxNum, finalFetches.size());
+    LOG.info(stage.getId() + ", ScheduleHashShuffledFetches - Max num=" + maxNum + ", finalFetchURI=" + finalFetches.size());
+
+    if (groupingColumns == 0) {
+      determinedTaskNum = 1;
+      LOG.info(stage.getId() + ", No Grouping Column - determinedTaskNum is set to 1");
+    } else {
+      TableStats totalStat = computeChildBlocksStats(stage.getContext(), masterPlan, stage.getId());
+      if (totalStat.getNumRows() == 0) {
+        determinedTaskNum = 1;
+      }
+    }
+
+    // set the proper number of tasks to the estimated task num
+    if (channel.getShuffleType() == SCATTERED_HASH_SHUFFLE) {
+      scheduleScatteredHashShuffleFetches(schedulerContext, stage, intermediates,
+          scan.getTableName());
+    } else {
+      schedulerContext.setEstimatedTaskNum(determinedTaskNum);
+      // divide fetch uris into the the proper number of tasks according to volumes
+      scheduleFetchesByEvenDistributedVolumes(stage, finalFetches, scan.getTableName(), determinedTaskNum);
+      LOG.info(stage.getId() + ", DeterminedTaskNum : " + determinedTaskNum);
+    }
+  }
+
+  public static Pair<Long [], Map<String, List<FetchImpl>>[]> makeEvenDistributedFetchImpl(
+      Map<Integer, FetchGroupMeta> partitions, String tableName, int num) {
+
+    // Sort fetchGroupMeta in a descending order of data volumes.
+    List<FetchGroupMeta> fetchGroupMetaList = Lists.newArrayList(partitions.values());
+    Collections.sort(fetchGroupMetaList, new Comparator<FetchGroupMeta>() {
+      @Override
+      public int compare(FetchGroupMeta o1, FetchGroupMeta o2) {
+        return o1.getVolume() < o2.getVolume() ? 1 : (o1.getVolume() > o2.getVolume() ? -1 : 0);
+      }
+    });
+
+    // Initialize containers
+    Map<String, List<FetchImpl>>[] fetchesArray = new Map[num];
+    Long [] assignedVolumes = new Long[num];
+    // initialization
+    for (int i = 0; i < num; i++) {
+      fetchesArray[i] = new HashMap<String, List<FetchImpl>>();
+      assignedVolumes[i] = 0l;
+    }
+
+    // This algorithm assignes bigger first manner by using a sorted iterator. It is a kind of greedy manner.
+    // Its complexity is O(n). Since FetchGroup can be more than tens of thousands, we should consider its complexity.
+    // In terms of this point, it will show reasonable performance and results. even though it is not an optimal
+    // algorithm.
+    Iterator<FetchGroupMeta> iterator = fetchGroupMetaList.iterator();
+
+    int p = 0;
+    while(iterator.hasNext()) {
+      while (p < num && iterator.hasNext()) {
+        FetchGroupMeta fetchGroupMeta = iterator.next();
+        assignedVolumes[p] += fetchGroupMeta.getVolume();
+
+        TUtil.putCollectionToNestedList(fetchesArray[p], tableName, fetchGroupMeta.fetchUrls);
+        p++;
+      }
+
+      p = num - 1;
+      while (p > 0 && iterator.hasNext()) {
+        FetchGroupMeta fetchGroupMeta = iterator.next();
+        assignedVolumes[p] += fetchGroupMeta.getVolume();
+        TUtil.putCollectionToNestedList(fetchesArray[p], tableName, fetchGroupMeta.fetchUrls);
+
+        // While the current one is smaller than next one, it adds additional fetches to current one.
+        while(iterator.hasNext() && assignedVolumes[p - 1] > assignedVolumes[p]) {
+          FetchGroupMeta additionalFetchGroup = iterator.next();
+          assignedVolumes[p] += additionalFetchGroup.getVolume();
+          TUtil.putCollectionToNestedList(fetchesArray[p], tableName, additionalFetchGroup.fetchUrls);
+        }
+
+        p--;
+      }
+    }
+
+    return new Pair<Long[], Map<String, List<FetchImpl>>[]>(assignedVolumes, fetchesArray);
+  }
+
+  public static void scheduleFetchesByEvenDistributedVolumes(Stage stage, Map<Integer, FetchGroupMeta> partitions,
+                                                             String tableName, int num) {
+    Map<String, List<FetchImpl>>[] fetchsArray = makeEvenDistributedFetchImpl(partitions, tableName, num).getSecond();
+    // Schedule FetchImpls
+    for (Map<String, List<FetchImpl>> eachFetches : fetchsArray) {
+      Stage.scheduleFetches(stage, eachFetches);
+    }
+  }
+
+  // Scattered hash shuffle hashes the key columns and groups the hash keys associated with
+  // the same hash key. Then, if the volume of a group is larger
+  // than $DIST_QUERY_TABLE_PARTITION_VOLUME, it divides the group into more than two sub groups
+  // according to $DIST_QUERY_TABLE_PARTITION_VOLUME (default size = 256MB).
+  // As a result, each group size always becomes the less than or equal
+  // to $DIST_QUERY_TABLE_PARTITION_VOLUME. Finally, each subgroup is assigned to a query unit.
+  // It is usually used for writing partitioned tables.
+  public static void scheduleScatteredHashShuffleFetches(TaskSchedulerContext schedulerContext,
+       Stage stage, Map<ExecutionBlockId, List<IntermediateEntry>> intermediates,
+       String tableName) {
+    long splitVolume = StorageUnit.MB *
+        stage.getMasterPlan().getContext().getLong(SessionVars.TABLE_PARTITION_PER_SHUFFLE_SIZE);
+    long pageSize = StorageUnit.MB * 
+        stage.getContext().getConf().getIntVar(ConfVars.SHUFFLE_HASH_APPENDER_PAGE_VOLUME); // in bytes
+    if (pageSize >= splitVolume) {
+      throw new RuntimeException("tajo.dist-query.table-partition.task-volume-mb should be great than " +
+          "tajo.shuffle.hash.appender.page.volumn-mb");
+    }
+    List<List<FetchImpl>> fetches = new ArrayList<List<FetchImpl>>();
+
+    long totalIntermediateSize = 0L;
+    for (Entry<ExecutionBlockId, List<IntermediateEntry>> listEntry : intermediates.entrySet()) {
+      // merge by PartitionId
+      Map<Integer, List<IntermediateEntry>> partitionIntermMap = new HashMap<Integer, List<IntermediateEntry>>();
+      for (IntermediateEntry eachInterm: listEntry.getValue()) {
+        totalIntermediateSize += eachInterm.getVolume();
+        int partId = eachInterm.getPartId();
+        List<IntermediateEntry> partitionInterms = partitionIntermMap.get(partId);
+        if (partitionInterms == null) {
+          partitionInterms = TUtil.newList(eachInterm);
+          partitionIntermMap.put(partId, partitionInterms);
+        } else {
+          partitionInterms.add(eachInterm);
+        }
+      }
+
+      // Grouping or splitting to fit $DIST_QUERY_TABLE_PARTITION_VOLUME size
+      for (List<IntermediateEntry> partitionEntries : partitionIntermMap.values()) {
+        List<List<FetchImpl>> eachFetches = splitOrMergeIntermediates(listEntry.getKey(), partitionEntries,
+            splitVolume, pageSize);
+        if (eachFetches != null && !eachFetches.isEmpty()) {
+          fetches.addAll(eachFetches);
+        }
+      }
+    }
+
+    schedulerContext.setEstimatedTaskNum(fetches.size());
+
+    int i = 0;
+    Map<String, List<FetchImpl>>[] fetchesArray = new Map[fetches.size()];
+    for(List<FetchImpl> entry : fetches) {
+      fetchesArray[i] = new HashMap<String, List<FetchImpl>>();
+      fetchesArray[i].put(tableName, entry);
+
+      Stage.scheduleFetches(stage, fetchesArray[i]);
+      i++;
+    }
+
+    LOG.info(stage.getId()
+        + ", ShuffleType:" + SCATTERED_HASH_SHUFFLE.name()
+        + ", Intermediate Size: " + totalIntermediateSize
+        + ", splitSize: " + splitVolume
+        + ", DeterminedTaskNum: " + fetches.size());
+  }
+
+  /**
+   * If a IntermediateEntry is large than splitVolume, List<FetchImpl> has single element.
+   * @param ebId
+   * @param entries
+   * @param splitVolume
+   * @return
+   */
+  public static List<List<FetchImpl>> splitOrMergeIntermediates(
+      ExecutionBlockId ebId, List<IntermediateEntry> entries, long splitVolume, long pageSize) {
+    // Each List<FetchImpl> has splitVolume size.
+    List<List<FetchImpl>> fetches = new ArrayList<List<FetchImpl>>();
+
+    Iterator<IntermediateEntry> iter = entries.iterator();
+    if (!iter.hasNext()) {
+      return null;
+    }
+    List<FetchImpl> fetchListForSingleTask = new ArrayList<FetchImpl>();
+    long fetchListVolume = 0;
+
+    while (iter.hasNext()) {
+      IntermediateEntry currentInterm = iter.next();
+
+      long firstSplitVolume = splitVolume - fetchListVolume;
+      if (firstSplitVolume < pageSize) {
+        firstSplitVolume = splitVolume;
+      }
+
+      //Each Pair object in the splits variable is assigned to the next ExectionBlock's task.
+      //The first long value is a offset of the intermediate file and the second long value is length.
+      List<Pair<Long, Long>> splits = currentInterm.split(firstSplitVolume, splitVolume);
+      if (splits == null || splits.isEmpty()) {
+        break;
+      }
+
+      for (Pair<Long, Long> eachSplit: splits) {
+        if (fetchListVolume > 0 && fetchListVolume + eachSplit.getSecond() >= splitVolume) {
+          if (!fetchListForSingleTask.isEmpty()) {
+            fetches.add(fetchListForSingleTask);
+          }
+          fetchListForSingleTask = new ArrayList<FetchImpl>();
+          fetchListVolume = 0;
+        }
+        FetchImpl fetch = new FetchImpl(currentInterm.getPullHost(), SCATTERED_HASH_SHUFFLE,
+            ebId, currentInterm.getPartId(), TUtil.newList(currentInterm));
+        fetch.setOffset(eachSplit.getFirst());
+        fetch.setLength(eachSplit.getSecond());
+        fetchListForSingleTask.add(fetch);
+        fetchListVolume += eachSplit.getSecond();
+      }
+    }
+    if (!fetchListForSingleTask.isEmpty()) {
+      fetches.add(fetchListForSingleTask);
+    }
+    return fetches;
+  }
+
+  public static List<URI> createFetchURL(FetchImpl fetch, boolean includeParts) {
+    String scheme = "http://";
+
+    StringBuilder urlPrefix = new StringBuilder(scheme);
+    urlPrefix.append(fetch.getPullHost().getHost()).append(":").append(fetch.getPullHost().getPort()).append("/?")
+        .append("qid=").append(fetch.getExecutionBlockId().getQueryId().toString())
+        .append("&sid=").append(fetch.getExecutionBlockId().getId())
+        .append("&p=").append(fetch.getPartitionId())
+        .append("&type=");
+    if (fetch.getType() == HASH_SHUFFLE) {
+      urlPrefix.append("h");
+    } else if (fetch.getType() == RANGE_SHUFFLE) {
+      urlPrefix.append("r").append("&").append(fetch.getRangeParams());
+    } else if (fetch.getType() == SCATTERED_HASH_SHUFFLE) {
+      urlPrefix.append("s");
+    }
+
+    if (fetch.getLength() >= 0) {
+      urlPrefix.append("&offset=").append(fetch.getOffset()).append("&length=").append(fetch.getLength());
+    }
+
+    List<URI> fetchURLs = new ArrayList<URI>();
+    if(includeParts) {
+      if (fetch.getType() == HASH_SHUFFLE || fetch.getType() == SCATTERED_HASH_SHUFFLE) {
+        fetchURLs.add(URI.create(urlPrefix.toString()));
+      } else {
+        // If the get request is longer than 2000 characters,
+        // the long request uri may cause HTTP Status Code - 414 Request-URI Too Long.
+        // Refer to http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.4.15
+        // The below code transforms a long request to multiple requests.
+        List<String> taskIdsParams = new ArrayList<String>();
+        StringBuilder taskIdListBuilder = new StringBuilder();
+        List<Integer> taskIds = fetch.getTaskIds();
+        List<Integer> attemptIds = fetch.getAttemptIds();
+        boolean first = true;
+
+        for (int i = 0; i < taskIds.size(); i++) {
+          StringBuilder taskAttemptId = new StringBuilder();
+
+          if (!first) { // when comma is added?
+            taskAttemptId.append(",");
+          } else {
+            first = false;
+          }
+
+          int taskId = taskIds.get(i);
+          if (taskId < 0) {
+            // In the case of hash shuffle each partition has single shuffle file per worker.
+            // TODO If file is large, consider multiple fetching(shuffle file can be split)
+            continue;
+          }
+          int attemptId = attemptIds.get(i);
+          taskAttemptId.append(taskId).append("_").append(attemptId);
+
+          if (taskIdListBuilder.length() + taskAttemptId.length()
+              > HTTP_REQUEST_MAXIMUM_LENGTH) {
+            taskIdsParams.add(taskIdListBuilder.toString());
+            taskIdListBuilder = new StringBuilder(taskId + "_" + attemptId);
+          } else {
+            taskIdListBuilder.append(taskAttemptId);
+          }
+        }
+        // if the url params remain
+        if (taskIdListBuilder.length() > 0) {
+          taskIdsParams.add(taskIdListBuilder.toString());
+        }
+        urlPrefix.append("&ta=");
+        for (String param : taskIdsParams) {
+          fetchURLs.add(URI.create(urlPrefix + param));
+        }
+      }
+    } else {
+      fetchURLs.add(URI.create(urlPrefix.toString()));
+    }
+
+    return fetchURLs;
+  }
+
+  public static Map<Integer, List<IntermediateEntry>> hashByKey(List<IntermediateEntry> entries) {
+    Map<Integer, List<IntermediateEntry>> hashed = new HashMap<Integer, List<IntermediateEntry>>();
+    for (IntermediateEntry entry : entries) {
+      if (hashed.containsKey(entry.getPartId())) {
+        hashed.get(entry.getPartId()).add(entry);
+      } else {
+        hashed.put(entry.getPartId(), TUtil.newList(entry));
+      }
+    }
+
+    return hashed;
+  }
+
+  public static Map<Task.PullHost, List<IntermediateEntry>> hashByHost(List<IntermediateEntry> entries) {
+    Map<Task.PullHost, List<IntermediateEntry>> hashed = new HashMap<Task.PullHost, List<IntermediateEntry>>();
+
+    Task.PullHost host;
+    for (IntermediateEntry entry : entries) {
+      host = entry.getPullHost();
+      if (hashed.containsKey(host)) {
+        hashed.get(host).add(entry);
+      } else {
+        hashed.put(host, TUtil.newList(entry));
+      }
+    }
+
+    return hashed;
+  }
+
+  public static Stage setShuffleOutputNumForTwoPhase(Stage stage, final int desiredNum, DataChannel channel) {
+    ExecutionBlock execBlock = stage.getBlock();
+    Column[] keys;
+    // if the next query is join,
+    // set the partition number for the current logicalUnit
+    // TODO: the union handling is required when a join has unions as its child
+    MasterPlan masterPlan = stage.getMasterPlan();
+    keys = channel.getShuffleKeys();
+    if (!masterPlan.isRoot(stage.getBlock()) ) {
+      ExecutionBlock parentBlock = masterPlan.getParent(stage.getBlock());
+      if (parentBlock.getPlan().getType() == NodeType.JOIN) {
+        channel.setShuffleOutputNum(desiredNum);
+      }
+    }
+
+    // set the partition number for group by and sort
+    if (channel.getShuffleType() == HASH_SHUFFLE) {
+      if (execBlock.getPlan().getType() == NodeType.GROUP_BY ||
+          execBlock.getPlan().getType() == NodeType.DISTINCT_GROUP_BY) {
+        keys = channel.getShuffleKeys();
+      }
+    } else if (channel.getShuffleType() == RANGE_SHUFFLE) {
+      if (execBlock.getPlan().getType() == NodeType.SORT) {
+        SortNode sort = (SortNode) execBlock.getPlan();
+        keys = new Column[sort.getSortKeys().length];
+        for (int i = 0; i < keys.length; i++) {
+          keys[i] = sort.getSortKeys()[i].getSortKey();
+        }
+      }
+    }
+    if (keys != null) {
+      if (keys.length == 0) {
+        channel.setShuffleKeys(new Column[]{});
+        channel.setShuffleOutputNum(1);
+      } else {
+        channel.setShuffleKeys(keys);
+        channel.setShuffleOutputNum(desiredNum);
+      }
+    }
+    return stage;
+  }
+}


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