diff --git a/hyracks-fullstack/algebricks/algebricks-compiler/src/main/java/org/apache/hyracks/algebricks/compiler/api/HeuristicCompilerFactoryBuilder.java b/hyracks-fullstack/algebricks/algebricks-compiler/src/main/java/org/apache/hyracks/algebricks/compiler/api/HeuristicCompilerFactoryBuilder.java
index 79b8f38..2d6123e 100644
--- a/hyracks-fullstack/algebricks/algebricks-compiler/src/main/java/org/apache/hyracks/algebricks/compiler/api/HeuristicCompilerFactoryBuilder.java
+++ b/hyracks-fullstack/algebricks/algebricks-compiler/src/main/java/org/apache/hyracks/algebricks/compiler/api/HeuristicCompilerFactoryBuilder.java
@@ -104,7 +104,7 @@
                                 clusterLocations);
 
                         PlanCompiler pc = new PlanCompiler(context);
-                        return pc.compilePlan(plan, null, jobEventListenerFactory);
+                        return pc.compilePlan(plan, jobEventListenerFactory);
                     }
                 };
             }
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/base/PhysicalOperatorTag.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/base/PhysicalOperatorTag.java
index 75b63f1..db9728b 100644
--- a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/base/PhysicalOperatorTag.java
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/base/PhysicalOperatorTag.java
@@ -44,6 +44,7 @@
     MATERIALIZE,
     MICRO_PRE_CLUSTERED_GROUP_BY,
     MICRO_PRE_SORTED_DISTINCT_BY,
+    MICRO_UNION_ALL,
     NESTED_LOOP,
     NESTED_TUPLE_SOURCE,
     ONE_TO_ONE_EXCHANGE,
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/AbstractPhysicalOperator.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/AbstractPhysicalOperator.java
index 43cde22..29d6037 100644
--- a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/AbstractPhysicalOperator.java
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/AbstractPhysicalOperator.java
@@ -18,6 +18,8 @@
  */
 package org.apache.hyracks.algebricks.core.algebra.operators.physical;
 
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Map;
 
 import org.apache.hyracks.algebricks.common.constraints.AlgebricksCountPartitionConstraint;
@@ -97,7 +99,7 @@
 
     /**
      * @return labels (0 or 1) for each input and output indicating the dependency between them.
-     *         The edges labeled as 1 must wait for the edges with label 0.
+     * The edges labeled as 1 must wait for the edges with label 0.
      */
     @Override
     public Pair<int[], int[]> getInputOutputDependencyLabels(ILogicalOperator op) {
@@ -118,47 +120,61 @@
     protected AlgebricksPipeline[] compileSubplans(IOperatorSchema outerPlanSchema,
             AbstractOperatorWithNestedPlans npOp, IOperatorSchema opSchema, JobGenContext context)
             throws AlgebricksException {
-        AlgebricksPipeline[] subplans = new AlgebricksPipeline[npOp.getNestedPlans().size()];
+        List<List<AlgebricksPipeline>> subplans = compileSubplansImpl(outerPlanSchema, npOp, opSchema, context);
+        int n = subplans.size();
+        AlgebricksPipeline[] result = new AlgebricksPipeline[n];
+        for (int i = 0; i < n; i++) {
+            List<AlgebricksPipeline> subplanOps = subplans.get(i);
+            if (subplanOps.size() != 1) {
+                throw new AlgebricksException("Attempting to construct a nested plan with " + subplanOps.size()
+                        + " operator descriptors. Currently, nested plans can only consist in linear pipelines of "
+                        + "micro operators.");
+            }
+            result[i] = subplanOps.get(0);
+        }
+        return result;
+    }
+
+    protected List<List<AlgebricksPipeline>> compileSubplansImpl(IOperatorSchema outerPlanSchema,
+            AbstractOperatorWithNestedPlans npOp, IOperatorSchema opSchema, JobGenContext context)
+            throws AlgebricksException {
+        List<List<AlgebricksPipeline>> subplans = new ArrayList<>(npOp.getNestedPlans().size());
         PlanCompiler pc = new PlanCompiler(context);
-        int i = 0;
         for (ILogicalPlan p : npOp.getNestedPlans()) {
-            subplans[i++] = buildPipelineWithProjection(p, outerPlanSchema, npOp, opSchema, pc);
+            subplans.add(buildPipelineWithProjection(p, outerPlanSchema, npOp, opSchema, pc));
         }
         return subplans;
     }
 
-    private AlgebricksPipeline buildPipelineWithProjection(ILogicalPlan p, IOperatorSchema outerPlanSchema,
+    private List<AlgebricksPipeline> buildPipelineWithProjection(ILogicalPlan p, IOperatorSchema outerPlanSchema,
             AbstractOperatorWithNestedPlans npOp, IOperatorSchema opSchema, PlanCompiler pc)
             throws AlgebricksException {
         if (p.getRoots().size() > 1) {
             throw new NotImplementedException("Nested plans with several roots are not supported.");
         }
-        JobSpecification nestedJob = pc.compilePlan(p, outerPlanSchema, null);
+        JobSpecification nestedJob = pc.compileNestedPlan(p, outerPlanSchema);
         ILogicalOperator topOpInSubplan = p.getRoots().get(0).getValue();
         JobGenContext context = pc.getContext();
         IOperatorSchema topOpInSubplanScm = context.getSchema(topOpInSubplan);
         opSchema.addAllVariables(topOpInSubplanScm);
 
         Map<OperatorDescriptorId, IOperatorDescriptor> opMap = nestedJob.getOperatorMap();
-        if (opMap.size() != 1) {
-            throw new AlgebricksException("Attempting to construct a nested plan with " + opMap.size()
-                    + " operator descriptors. Currently, nested plans can only consist in linear pipelines of Asterix micro operators.");
-        }
-
-        for (Map.Entry<OperatorDescriptorId, IOperatorDescriptor> opEntry : opMap.entrySet()) {
-            IOperatorDescriptor opd = opEntry.getValue();
-            if (!(opd instanceof AlgebricksMetaOperatorDescriptor)) {
-                throw new AlgebricksException(
-                        "Can only generate Hyracks jobs for pipelinable Asterix nested plans, not for "
-                                + opd.getClass().getName());
+        List<? extends IOperatorDescriptor> metaOps = nestedJob.getMetaOps();
+        if (opMap.size() != metaOps.size()) {
+            for (IOperatorDescriptor opd : opMap.values()) {
+                if (!(opd instanceof AlgebricksMetaOperatorDescriptor)) {
+                    throw new AlgebricksException(
+                            "Can only generate jobs for pipelinable nested plans, not for " + opd.getClass().getName());
+                }
             }
-            AlgebricksMetaOperatorDescriptor amod = (AlgebricksMetaOperatorDescriptor) opd;
-
-            return amod.getPipeline();
-            // we suppose that the top operator in the subplan already does the
-            // projection for us
+            throw new IllegalStateException("Unexpected nested plan");
         }
 
-        throw new IllegalStateException();
+        List<AlgebricksPipeline> result = new ArrayList<>(metaOps.size());
+        for (IOperatorDescriptor opd : metaOps) {
+            AlgebricksMetaOperatorDescriptor amod = (AlgebricksMetaOperatorDescriptor) opd;
+            result.add(amod.getPipeline());
+        }
+        return result;
     }
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/AbstractUnionAllPOperator.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/AbstractUnionAllPOperator.java
new file mode 100644
index 0000000..a4d9576
--- /dev/null
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/AbstractUnionAllPOperator.java
@@ -0,0 +1,78 @@
+/*
+ * 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.hyracks.algebricks.core.algebra.operators.physical;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.commons.lang3.mutable.Mutable;
+import org.apache.hyracks.algebricks.common.exceptions.AlgebricksException;
+import org.apache.hyracks.algebricks.core.algebra.base.IHyracksJobBuilder;
+import org.apache.hyracks.algebricks.core.algebra.base.ILogicalOperator;
+import org.apache.hyracks.algebricks.core.algebra.base.IOptimizationContext;
+import org.apache.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
+import org.apache.hyracks.algebricks.core.algebra.operators.logical.IOperatorSchema;
+import org.apache.hyracks.algebricks.core.algebra.properties.IPartitioningProperty;
+import org.apache.hyracks.algebricks.core.algebra.properties.IPartitioningRequirementsCoordinator;
+import org.apache.hyracks.algebricks.core.algebra.properties.IPhysicalPropertiesVector;
+import org.apache.hyracks.algebricks.core.algebra.properties.PhysicalRequirements;
+import org.apache.hyracks.algebricks.core.algebra.properties.RandomPartitioningProperty;
+import org.apache.hyracks.algebricks.core.algebra.properties.StructuralPropertiesVector;
+import org.apache.hyracks.algebricks.core.algebra.util.OperatorPropertiesUtil;
+import org.apache.hyracks.algebricks.core.jobgen.impl.JobGenContext;
+
+public abstract class AbstractUnionAllPOperator extends AbstractPhysicalOperator {
+
+    @Override
+    public void computeDeliveredProperties(ILogicalOperator op, IOptimizationContext context) {
+        AbstractLogicalOperator op2 = (AbstractLogicalOperator) op.getInputs().get(0).getValue();
+        IPartitioningProperty pp = op2.getDeliveredPhysicalProperties().getPartitioningProperty();
+        this.deliveredProperties = new StructuralPropertiesVector(pp, new ArrayList<>(0));
+    }
+
+    @Override
+    public PhysicalRequirements getRequiredPropertiesForChildren(ILogicalOperator op,
+            IPhysicalPropertiesVector reqdByParent, IOptimizationContext context) {
+        StructuralPropertiesVector pv0 =
+                OperatorPropertiesUtil.checkUnpartitionedAndGetPropertiesVector(op, new StructuralPropertiesVector(
+                        new RandomPartitioningProperty(context.getComputationNodeDomain()), null));
+        StructuralPropertiesVector pv1 =
+                OperatorPropertiesUtil.checkUnpartitionedAndGetPropertiesVector(op, new StructuralPropertiesVector(
+                        new RandomPartitioningProperty(context.getComputationNodeDomain()), null));
+        return new PhysicalRequirements(new StructuralPropertiesVector[] { pv0, pv1 },
+                IPartitioningRequirementsCoordinator.NO_COORDINATION);
+    }
+
+    @Override
+    public boolean expensiveThanMaterialization() {
+        return false;
+    }
+
+    @Override
+    public void contributeRuntimeOperator(IHyracksJobBuilder builder, JobGenContext context, ILogicalOperator op,
+            IOperatorSchema opSchema, IOperatorSchema[] inputSchemas, IOperatorSchema outerPlanSchema)
+            throws AlgebricksException {
+        List<Mutable<ILogicalOperator>> inputs = op.getInputs();
+        for (int i = 0; i < inputs.size(); i++) {
+            ILogicalOperator src = inputs.get(i).getValue();
+            builder.contributeGraphEdge(src, 0, op, i);
+        }
+    }
+}
\ No newline at end of file
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/MicroUnionAllPOperator.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/MicroUnionAllPOperator.java
new file mode 100644
index 0000000..f5e992e
--- /dev/null
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/MicroUnionAllPOperator.java
@@ -0,0 +1,56 @@
+/*
+ * 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.hyracks.algebricks.core.algebra.operators.physical;
+
+import org.apache.hyracks.algebricks.common.exceptions.AlgebricksException;
+import org.apache.hyracks.algebricks.core.algebra.base.IHyracksJobBuilder;
+import org.apache.hyracks.algebricks.core.algebra.base.ILogicalOperator;
+import org.apache.hyracks.algebricks.core.algebra.base.PhysicalOperatorTag;
+import org.apache.hyracks.algebricks.core.algebra.operators.logical.IOperatorSchema;
+import org.apache.hyracks.algebricks.core.jobgen.impl.JobGenContext;
+import org.apache.hyracks.algebricks.core.jobgen.impl.JobGenHelper;
+import org.apache.hyracks.algebricks.runtime.operators.union.MicroUnionAllRuntimeFactory;
+import org.apache.hyracks.api.dataflow.value.RecordDescriptor;
+
+public class MicroUnionAllPOperator extends AbstractUnionAllPOperator {
+
+    @Override
+    public PhysicalOperatorTag getOperatorTag() {
+        return PhysicalOperatorTag.MICRO_UNION_ALL;
+    }
+
+    @Override
+    public boolean isMicroOperator() {
+        return true;
+    }
+
+    @Override
+    public void contributeRuntimeOperator(IHyracksJobBuilder builder, JobGenContext context, ILogicalOperator op,
+            IOperatorSchema opSchema, IOperatorSchema[] inputSchemas, IOperatorSchema outerPlanSchema)
+            throws AlgebricksException {
+        RecordDescriptor recordDescriptor =
+                JobGenHelper.mkRecordDescriptor(context.getTypeEnvironment(op), opSchema, context);
+
+        MicroUnionAllRuntimeFactory runtime = new MicroUnionAllRuntimeFactory(op.getInputs().size());
+        builder.contributeMicroOperator(op, runtime, recordDescriptor);
+
+        super.contributeRuntimeOperator(builder, context, op, opSchema, inputSchemas, outerPlanSchema);
+    }
+}
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/SubplanPOperator.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/SubplanPOperator.java
index d43ddab..95efbac 100644
--- a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/SubplanPOperator.java
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/SubplanPOperator.java
@@ -89,18 +89,18 @@
         if (subplan.getNestedPlans().size() != 1) {
             throw new NotImplementedException("Subplan currently works only for one nested plan with one root.");
         }
-        AlgebricksPipeline[] subplans = compileSubplans(inputSchemas[0], subplan, opSchema, context);
-        assert subplans.length == 1;
-        AlgebricksPipeline np = subplans[0];
+        List<List<AlgebricksPipeline>> subplans = compileSubplansImpl(inputSchemas[0], subplan, opSchema, context);
+        assert subplans.size() == 1;
+        List<AlgebricksPipeline> np = subplans.get(0);
         RecordDescriptor inputRecordDesc = JobGenHelper.mkRecordDescriptor(
                 context.getTypeEnvironment(op.getInputs().get(0).getValue()), inputSchemas[0], context);
-        IMissingWriterFactory[] missingWriterFactories = new IMissingWriterFactory[np.getOutputWidth()];
+        IMissingWriterFactory[] missingWriterFactories = new IMissingWriterFactory[np.get(0).getOutputWidth()];
         for (int i = 0; i < missingWriterFactories.length; i++) {
             missingWriterFactories[i] = context.getMissingWriterFactory();
         }
-        SubplanRuntimeFactory runtime = new SubplanRuntimeFactory(np, missingWriterFactories, inputRecordDesc, null);
-
         RecordDescriptor recDesc = JobGenHelper.mkRecordDescriptor(context.getTypeEnvironment(op), opSchema, context);
+        SubplanRuntimeFactory runtime =
+                new SubplanRuntimeFactory(np, missingWriterFactories, inputRecordDesc, recDesc, null);
         builder.contributeMicroOperator(subplan, runtime, recDesc);
 
         ILogicalOperator src = op.getInputs().get(0).getValue();
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/UnionAllPOperator.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/UnionAllPOperator.java
index a617064..4ccce92 100644
--- a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/UnionAllPOperator.java
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/operators/physical/UnionAllPOperator.java
@@ -18,29 +18,18 @@
  */
 package org.apache.hyracks.algebricks.core.algebra.operators.physical;
 
-import java.util.ArrayList;
-
 import org.apache.hyracks.algebricks.common.exceptions.AlgebricksException;
 import org.apache.hyracks.algebricks.core.algebra.base.IHyracksJobBuilder;
 import org.apache.hyracks.algebricks.core.algebra.base.ILogicalOperator;
-import org.apache.hyracks.algebricks.core.algebra.base.IOptimizationContext;
 import org.apache.hyracks.algebricks.core.algebra.base.PhysicalOperatorTag;
 import org.apache.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.logical.IOperatorSchema;
-import org.apache.hyracks.algebricks.core.algebra.properties.IPartitioningProperty;
-import org.apache.hyracks.algebricks.core.algebra.properties.IPartitioningRequirementsCoordinator;
-import org.apache.hyracks.algebricks.core.algebra.properties.IPhysicalPropertiesVector;
-import org.apache.hyracks.algebricks.core.algebra.properties.PhysicalRequirements;
-import org.apache.hyracks.algebricks.core.algebra.properties.RandomPartitioningProperty;
-import org.apache.hyracks.algebricks.core.algebra.properties.StructuralPropertiesVector;
-import org.apache.hyracks.algebricks.core.algebra.util.OperatorPropertiesUtil;
 import org.apache.hyracks.algebricks.core.jobgen.impl.JobGenContext;
 import org.apache.hyracks.algebricks.core.jobgen.impl.JobGenHelper;
 import org.apache.hyracks.api.dataflow.value.RecordDescriptor;
-import org.apache.hyracks.api.job.IOperatorDescriptorRegistry;
 import org.apache.hyracks.dataflow.std.union.UnionAllOperatorDescriptor;
 
-public class UnionAllPOperator extends AbstractPhysicalOperator {
+public class UnionAllPOperator extends AbstractUnionAllPOperator {
 
     @Override
     public PhysicalOperatorTag getOperatorTag() {
@@ -53,48 +42,16 @@
     }
 
     @Override
-    public void computeDeliveredProperties(ILogicalOperator op, IOptimizationContext context) {
-        AbstractLogicalOperator op2 = (AbstractLogicalOperator) op.getInputs().get(0).getValue();
-        IPartitioningProperty pp = op2.getDeliveredPhysicalProperties().getPartitioningProperty();
-        this.deliveredProperties = new StructuralPropertiesVector(pp, new ArrayList<>(0));
-    }
-
-    @Override
-    public PhysicalRequirements getRequiredPropertiesForChildren(ILogicalOperator op,
-            IPhysicalPropertiesVector reqdByParent, IOptimizationContext context) {
-        StructuralPropertiesVector pv0 =
-                OperatorPropertiesUtil.checkUnpartitionedAndGetPropertiesVector(op, new StructuralPropertiesVector(
-                        new RandomPartitioningProperty(context.getComputationNodeDomain()), null));
-        StructuralPropertiesVector pv1 =
-                OperatorPropertiesUtil.checkUnpartitionedAndGetPropertiesVector(op, new StructuralPropertiesVector(
-                        new RandomPartitioningProperty(context.getComputationNodeDomain()), null));
-        return new PhysicalRequirements(new StructuralPropertiesVector[] { pv0, pv1 },
-                IPartitioningRequirementsCoordinator.NO_COORDINATION);
-    }
-
-    @Override
     public void contributeRuntimeOperator(IHyracksJobBuilder builder, JobGenContext context, ILogicalOperator op,
             IOperatorSchema opSchema, IOperatorSchema[] inputSchemas, IOperatorSchema outerPlanSchema)
             throws AlgebricksException {
-
-        IOperatorDescriptorRegistry spec = builder.getJobSpec();
         RecordDescriptor recordDescriptor =
                 JobGenHelper.mkRecordDescriptor(context.getTypeEnvironment(op), opSchema, context);
 
-        // at algebricks level, union all only accepts two inputs, although at
-        // hyracks
-        // level, there is no restrictions
-        UnionAllOperatorDescriptor opDesc = new UnionAllOperatorDescriptor(spec, 2, recordDescriptor);
+        UnionAllOperatorDescriptor opDesc =
+                new UnionAllOperatorDescriptor(builder.getJobSpec(), op.getInputs().size(), recordDescriptor);
         contributeOpDesc(builder, (AbstractLogicalOperator) op, opDesc);
-        ILogicalOperator src1 = op.getInputs().get(0).getValue();
-        builder.contributeGraphEdge(src1, 0, op, 0);
-        ILogicalOperator src2 = op.getInputs().get(1).getValue();
-        builder.contributeGraphEdge(src2, 0, op, 1);
-    }
 
-    @Override
-    public boolean expensiveThanMaterialization() {
-        return false;
+        super.contributeRuntimeOperator(builder, context, op, opSchema, inputSchemas, outerPlanSchema);
     }
-
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/util/OperatorManipulationUtil.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/util/OperatorManipulationUtil.java
index 249e66f..c574cd8 100644
--- a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/util/OperatorManipulationUtil.java
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/algebra/util/OperatorManipulationUtil.java
@@ -18,7 +18,10 @@
  */
 package org.apache.hyracks.algebricks.core.algebra.util;
 
+import java.util.ArrayDeque;
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Deque;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -202,7 +205,7 @@
     public static Pair<ILogicalOperator, Map<LogicalVariable, LogicalVariable>> deepCopyWithNewVars(
             ILogicalOperator root, IOptimizationContext ctx) throws AlgebricksException {
         LogicalOperatorDeepCopyWithNewVariablesVisitor deepCopyVisitor =
-                new LogicalOperatorDeepCopyWithNewVariablesVisitor(ctx, null, true);
+                new LogicalOperatorDeepCopyWithNewVariablesVisitor(ctx, ctx, true);
         ILogicalOperator newRoot = deepCopyVisitor.deepCopy(root);
         return Pair.of(newRoot, deepCopyVisitor.getInputToOutputVariableMapping());
     }
@@ -327,4 +330,45 @@
         return false;
     }
 
+    /**
+     * Returns all descendants of an operator that are leaf operators
+     *
+     * @param opRef given operator
+     * @return list containing all leaf descendants
+     */
+    public static List<Mutable<ILogicalOperator>> findLeafDescendantsOrSelf(Mutable<ILogicalOperator> opRef) {
+        List<Mutable<ILogicalOperator>> result = Collections.emptyList();
+
+        Deque<Mutable<ILogicalOperator>> queue = new ArrayDeque<>();
+        queue.add(opRef);
+        Mutable<ILogicalOperator> currentOpRef;
+        while ((currentOpRef = queue.pollLast()) != null) {
+            List<Mutable<ILogicalOperator>> inputs = currentOpRef.getValue().getInputs();
+            if (inputs.isEmpty()) {
+                if (result.isEmpty()) {
+                    result = new ArrayList<>();
+                }
+                result.add(currentOpRef);
+            } else {
+                queue.addAll(inputs);
+            }
+        }
+        return result;
+    }
+
+    /**
+     * Find operator in a given list of operator references
+     *
+     * @param list list to search in
+     * @param op   operator to find
+     * @return operator position in the given list or {@code -1} if not found
+     */
+    public static int indexOf(List<Mutable<ILogicalOperator>> list, ILogicalOperator op) {
+        for (int i = 0, ln = list.size(); i < ln; i++) {
+            if (list.get(i).getValue() == op) {
+                return i;
+            }
+        }
+        return -1;
+    }
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/jobgen/impl/JobBuilder.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/jobgen/impl/JobBuilder.java
index 13eef09..16992e7 100644
--- a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/jobgen/impl/JobBuilder.java
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/jobgen/impl/JobBuilder.java
@@ -23,6 +23,7 @@
 import java.util.List;
 import java.util.Map;
 
+import org.apache.commons.lang3.ArrayUtils;
 import org.apache.hyracks.algebricks.common.constraints.AlgebricksAbsolutePartitionConstraint;
 import org.apache.hyracks.algebricks.common.constraints.AlgebricksCountPartitionConstraint;
 import org.apache.hyracks.algebricks.common.constraints.AlgebricksPartitionConstraint;
@@ -34,6 +35,8 @@
 import org.apache.hyracks.algebricks.core.algebra.base.ILogicalOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.logical.AbstractLogicalOperator.ExecutionMode;
+import org.apache.hyracks.algebricks.core.algebra.util.OperatorManipulationUtil;
+import org.apache.hyracks.algebricks.runtime.base.AlgebricksPipeline;
 import org.apache.hyracks.algebricks.runtime.base.IPushRuntimeFactory;
 import org.apache.hyracks.algebricks.runtime.operators.meta.AlgebricksMetaOperatorDescriptor;
 import org.apache.hyracks.api.dataflow.ConnectorDescriptorId;
@@ -96,7 +99,7 @@
     @Override
     public void contributeMicroOperator(ILogicalOperator op, IPushRuntimeFactory runtime, RecordDescriptor recDesc,
             AlgebricksPartitionConstraint pc) {
-        microOps.put(op, new Pair<IPushRuntimeFactory, RecordDescriptor>(runtime, recDesc));
+        microOps.put(op, new Pair<>(runtime, recDesc));
         revMicroOpMap.put(runtime, op);
         if (pc != null) {
             pcForMicroOps.put(op, pc);
@@ -171,6 +174,17 @@
         setAllPartitionConstraints(tgtConstraints);
     }
 
+    public List<IOperatorDescriptor> getGeneratedMetaOps() {
+        List<IOperatorDescriptor> resultOps = new ArrayList<>();
+        for (IOperatorDescriptor opd : jobSpec.getOperatorMap().values()) {
+            if (opd instanceof AlgebricksMetaOperatorDescriptor) {
+                resultOps.add(opd);
+            }
+        }
+        resultOps.sort((op1, op2) -> sendsOutput(op1, op2) ? 1 : sendsOutput(op2, op1) ? -1 : 0);
+        return resultOps;
+    }
+
     private void setAllPartitionConstraints(Map<IConnectorDescriptor, TargetConstraint> tgtConstraints) {
         List<OperatorDescriptorId> roots = jobSpec.getRoots();
         setSpecifiedPartitionConstraints();
@@ -317,20 +331,30 @@
         int n = opContents.size();
         IPushRuntimeFactory[] runtimeFactories = new IPushRuntimeFactory[n];
         RecordDescriptor[] internalRecordDescriptors = new RecordDescriptor[n];
-        int i = 0;
-        for (Pair<IPushRuntimeFactory, RecordDescriptor> p : opContents) {
+        for (int i = 0, ln = opContents.size(); i < ln; i++) {
+            Pair<IPushRuntimeFactory, RecordDescriptor> p = opContents.get(i);
             runtimeFactories[i] = p.first;
             internalRecordDescriptors[i] = p.second;
-            i++;
         }
         ILogicalOperator lastLogicalOp = revMicroOpMap.get(runtimeFactories[n - 1]);
         ArrayList<ILogicalOperator> outOps = outEdges.get(lastLogicalOp);
-        int outArity = (outOps == null) ? 0 : outOps.size();
+        int outArity = outOps == null ? 0 : outOps.size();
+        int[] outPositions = new int[outArity];
+        IPushRuntimeFactory[] outRuntimeFactories = new IPushRuntimeFactory[outArity];
+        if (outOps != null) {
+            for (int i = 0, ln = outOps.size(); i < ln; i++) {
+                ILogicalOperator outOp = outOps.get(i);
+                outPositions[i] = OperatorManipulationUtil.indexOf(outOp.getInputs(), lastLogicalOp);
+                Pair<IPushRuntimeFactory, RecordDescriptor> microOpPair = microOps.get(outOp);
+                outRuntimeFactories[i] = microOpPair != null ? microOpPair.first : null;
+            }
+        }
+
         ILogicalOperator firstLogicalOp = revMicroOpMap.get(runtimeFactories[0]);
         ArrayList<ILogicalOperator> inOps = inEdges.get(firstLogicalOp);
         int inArity = (inOps == null) ? 0 : inOps.size();
         return new AlgebricksMetaOperatorDescriptor(jobSpec, inArity, outArity, runtimeFactories,
-                internalRecordDescriptors);
+                internalRecordDescriptors, outRuntimeFactories, outPositions);
     }
 
     private void addMicroOpToMetaRuntimeOp(ILogicalOperator aop) {
@@ -344,7 +368,12 @@
             return;
         }
         ILogicalOperator dest = destList.get(0);
+        int destInputPos = OperatorManipulationUtil.indexOf(dest.getInputs(), aop);
         Integer j = algebraicOpBelongingToMetaAsterixOp.get(dest);
+        if (destInputPos != 0) {
+            return;
+        }
+
         if (j == null && microOps.get(dest) != null) {
             algebraicOpBelongingToMetaAsterixOp.put(dest, k);
             List<Pair<IPushRuntimeFactory, RecordDescriptor>> aodContent1 = metaAsterixOpSkeletons.get(k);
@@ -362,7 +391,6 @@
                 }
             }
         }
-
     }
 
     private int createNewMetaOpInfo(ILogicalOperator aop) {
@@ -387,4 +415,28 @@
         }
     }
 
+    private boolean sendsOutput(IOperatorDescriptor src, IOperatorDescriptor trg) {
+        AlgebricksPipeline srcPipeline = ((AlgebricksMetaOperatorDescriptor) src).getPipeline();
+        IPushRuntimeFactory[] srcOutRts = srcPipeline.getOutputRuntimeFactories();
+        if (srcOutRts == null) {
+            return false;
+        }
+        IPushRuntimeFactory[] trgRts = ((AlgebricksMetaOperatorDescriptor) trg).getPipeline().getRuntimeFactories();
+        for (IPushRuntimeFactory srcOutRt : srcOutRts) {
+            if (ArrayUtils.contains(trgRts, srcOutRt)) {
+                return true;
+            }
+            ILogicalOperator srcOutOp = revMicroOpMap.get(srcOutRt);
+            if (srcOutOp != null) {
+                Integer k = algebraicOpBelongingToMetaAsterixOp.get(srcOutOp);
+                if (k != null) {
+                    AlgebricksMetaOperatorDescriptor srcOutMetaOp = metaAsterixOps.get(k);
+                    if (srcOutMetaOp != null && sendsOutput(srcOutMetaOp, trg)) {
+                        return true;
+                    }
+                }
+            }
+        }
+        return false;
+    }
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/jobgen/impl/PlanCompiler.java b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/jobgen/impl/PlanCompiler.java
index 7409247..ddda258 100644
--- a/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/jobgen/impl/PlanCompiler.java
+++ b/hyracks-fullstack/algebricks/algebricks-core/src/main/java/org/apache/hyracks/algebricks/core/jobgen/impl/PlanCompiler.java
@@ -48,14 +48,24 @@
         return context;
     }
 
-    public JobSpecification compilePlan(ILogicalPlan plan, IOperatorSchema outerPlanSchema,
+    public JobSpecification compilePlan(ILogicalPlan plan, IJobletEventListenerFactory jobEventListenerFactory)
+            throws AlgebricksException {
+        return compilePlanImpl(plan, false, null, jobEventListenerFactory);
+    }
+
+    public JobSpecification compileNestedPlan(ILogicalPlan plan, IOperatorSchema outerPlanSchema)
+            throws AlgebricksException {
+        return compilePlanImpl(plan, true, outerPlanSchema, null);
+    }
+
+    private JobSpecification compilePlanImpl(ILogicalPlan plan, boolean isNestedPlan, IOperatorSchema outerPlanSchema,
             IJobletEventListenerFactory jobEventListenerFactory) throws AlgebricksException {
         JobSpecification spec = new JobSpecification(context.getFrameSize());
         if (jobEventListenerFactory != null) {
             spec.setJobletEventListenerFactory(jobEventListenerFactory);
         }
-        List<ILogicalOperator> rootOps = new ArrayList<ILogicalOperator>();
-        IHyracksJobBuilder builder = new JobBuilder(spec, context.getClusterLocations());
+        List<ILogicalOperator> rootOps = new ArrayList<>();
+        JobBuilder builder = new JobBuilder(spec, context.getClusterLocations());
         for (Mutable<ILogicalOperator> opRef : plan.getRoots()) {
             compileOpRef(opRef, spec, builder, outerPlanSchema);
             rootOps.add(opRef.getValue());
@@ -66,6 +76,9 @@
         spec.setConnectorPolicyAssignmentPolicy(new ConnectorPolicyAssignmentPolicy());
         // Do not do activity cluster planning because it is slow on large clusters
         spec.setUseConnectorPolicyForScheduling(false);
+        if (isNestedPlan) {
+            spec.setMetaOps(builder.getGeneratedMetaOps());
+        }
         return spec;
     }
 
diff --git a/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/SetAlgebricksPhysicalOperatorsRule.java b/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/SetAlgebricksPhysicalOperatorsRule.java
index 5b6285a..d277043 100644
--- a/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/SetAlgebricksPhysicalOperatorsRule.java
+++ b/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/SetAlgebricksPhysicalOperatorsRule.java
@@ -67,6 +67,7 @@
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.LeftOuterUnnestPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.MicroPreSortedDistinctByPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.MicroPreclusteredGroupByPOperator;
+import org.apache.hyracks.algebricks.core.algebra.operators.physical.MicroUnionAllPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.NestedTupleSourcePOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.PreSortedDistinctByPOperator;
 import org.apache.hyracks.algebricks.core.algebra.operators.physical.PreclusteredGroupByPOperator;
@@ -200,11 +201,11 @@
                     break;
                 }
                 case INNERJOIN: {
-                    JoinUtils.setJoinAlgorithmAndExchangeAlgo((InnerJoinOperator) op, context);
+                    JoinUtils.setJoinAlgorithmAndExchangeAlgo((InnerJoinOperator) op, topLevelOp, context);
                     break;
                 }
                 case LEFTOUTERJOIN: {
-                    JoinUtils.setJoinAlgorithmAndExchangeAlgo((LeftOuterJoinOperator) op, context);
+                    JoinUtils.setJoinAlgorithmAndExchangeAlgo((LeftOuterJoinOperator) op, topLevelOp, context);
                     break;
                 }
                 case LIMIT: {
@@ -259,11 +260,19 @@
                     break;
                 }
                 case UNIONALL: {
-                    op.setPhysicalOperator(new UnionAllPOperator());
+                    if (topLevelOp) {
+                        op.setPhysicalOperator(new UnionAllPOperator());
+                    } else {
+                        op.setPhysicalOperator(new MicroUnionAllPOperator());
+                    }
                     break;
                 }
                 case INTERSECT: {
-                    op.setPhysicalOperator(new IntersectPOperator());
+                    if (topLevelOp) {
+                        op.setPhysicalOperator(new IntersectPOperator());
+                    } else {
+                        throw new IllegalStateException("Micro operator not implemented for: " + op.getOperatorTag());
+                    }
                     break;
                 }
                 case UNNEST: {
diff --git a/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/subplan/PushSubplanIntoGroupByRule.java b/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/subplan/PushSubplanIntoGroupByRule.java
index 9d3b311..3efa46b 100644
--- a/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/subplan/PushSubplanIntoGroupByRule.java
+++ b/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/rules/subplan/PushSubplanIntoGroupByRule.java
@@ -139,6 +139,10 @@
                 while (upperSubplanRootRefIterator.hasNext()) {
                     Mutable<ILogicalOperator> rootOpRef = upperSubplanRootRefIterator.next();
 
+                    if (downToNts(rootOpRef) == null) {
+                        continue;
+                    }
+
                     // Collects free variables in the root operator of a nested plan and its descent.
                     Set<LogicalVariable> freeVars = new ListSet<>();
                     OperatorPropertiesUtil.getFreeVariablesInSelfOrDesc((AbstractLogicalOperator) rootOpRef.getValue(),
@@ -154,6 +158,9 @@
                             // Sets the nts for a original subplan.
                             Mutable<ILogicalOperator> originalGbyRootOpRef = gbyNestedPlan.getRoots().get(rootIndex);
                             Mutable<ILogicalOperator> originalGbyNtsRef = downToNts(originalGbyRootOpRef);
+                            if (originalGbyNtsRef == null) {
+                                continue;
+                            }
                             NestedTupleSourceOperator originalNts =
                                     (NestedTupleSourceOperator) originalGbyNtsRef.getValue();
                             originalNts.setDataSourceReference(new MutableObject<>(gby));
@@ -265,11 +272,13 @@
     }
 
     private Mutable<ILogicalOperator> downToNts(Mutable<ILogicalOperator> opRef) {
-        Mutable<ILogicalOperator> currentOpRef = opRef;
-        while (currentOpRef.getValue().getInputs().size() > 0) {
-            currentOpRef = currentOpRef.getValue().getInputs().get(0);
+        List<Mutable<ILogicalOperator>> leafOps = OperatorManipulationUtil.findLeafDescendantsOrSelf(opRef);
+        if (leafOps.size() == 1) {
+            Mutable<ILogicalOperator> leafOp = leafOps.get(0);
+            if (leafOp.getValue().getOperatorTag() == LogicalOperatorTag.NESTEDTUPLESOURCE) {
+                return leafOp;
+            }
         }
-        return currentOpRef;
+        return null;
     }
-
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/util/JoinUtils.java b/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/util/JoinUtils.java
index 6efda52..0bc2a5e 100644
--- a/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/util/JoinUtils.java
+++ b/hyracks-fullstack/algebricks/algebricks-rewriter/src/main/java/org/apache/hyracks/algebricks/rewriter/util/JoinUtils.java
@@ -51,8 +51,11 @@
     private JoinUtils() {
     }
 
-    public static void setJoinAlgorithmAndExchangeAlgo(AbstractBinaryJoinOperator op, IOptimizationContext context)
-            throws AlgebricksException {
+    public static void setJoinAlgorithmAndExchangeAlgo(AbstractBinaryJoinOperator op, boolean topLevelOp,
+            IOptimizationContext context) throws AlgebricksException {
+        if (!topLevelOp) {
+            throw new IllegalStateException("Micro operator not implemented for: " + op.getOperatorTag());
+        }
         List<LogicalVariable> sideLeft = new LinkedList<>();
         List<LogicalVariable> sideRight = new LinkedList<>();
         List<LogicalVariable> varsLeft = op.getInputs().get(0).getValue().getSchema();
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/pom.xml b/hyracks-fullstack/algebricks/algebricks-runtime/pom.xml
index bbea2ab..dafb6ab 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/pom.xml
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/pom.xml
@@ -73,6 +73,10 @@
       <version>${project.version}</version>
     </dependency>
     <dependency>
+      <groupId>org.apache.commons</groupId>
+      <artifactId>commons-lang3</artifactId>
+    </dependency>
+    <dependency>
       <groupId>com.fasterxml.jackson.core</groupId>
       <artifactId>jackson-databind</artifactId>
     </dependency>
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/base/AlgebricksPipeline.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/base/AlgebricksPipeline.java
index 379944b..f24d38d 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/base/AlgebricksPipeline.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/base/AlgebricksPipeline.java
@@ -27,10 +27,15 @@
     private static final long serialVersionUID = 1L;
     private final IPushRuntimeFactory[] runtimeFactories;
     private final RecordDescriptor[] recordDescriptors;
+    private final IPushRuntimeFactory[] outputRuntimeFactories;
+    private final int[] outputPositions;
 
-    public AlgebricksPipeline(IPushRuntimeFactory[] runtimeFactories, RecordDescriptor[] recordDescriptors) {
+    public AlgebricksPipeline(IPushRuntimeFactory[] runtimeFactories, RecordDescriptor[] recordDescriptors,
+            IPushRuntimeFactory[] outputRuntimeFactories, int[] outputPositions) {
         this.runtimeFactories = runtimeFactories;
         this.recordDescriptors = recordDescriptors;
+        this.outputRuntimeFactories = outputRuntimeFactories;
+        this.outputPositions = outputPositions;
         // this.projectedColumns = projectedColumns;
     }
 
@@ -46,8 +51,15 @@
         return recordDescriptors[recordDescriptors.length - 1].getFieldCount();
     }
 
+    public IPushRuntimeFactory[] getOutputRuntimeFactories() {
+        return outputRuntimeFactories;
+    }
+
+    public int[] getOutputPositions() {
+        return outputPositions;
+    }
+
     // public int[] getProjectedColumns() {
     // return projectedColumns;
     // }
-
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/base/IPushRuntimeFactory.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/base/IPushRuntimeFactory.java
index de6cddd..f90de81 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/base/IPushRuntimeFactory.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/base/IPushRuntimeFactory.java
@@ -24,5 +24,5 @@
 import org.apache.hyracks.api.exceptions.HyracksDataException;
 
 public interface IPushRuntimeFactory extends Serializable {
-    public IPushRuntime createPushRuntime(IHyracksTaskContext ctx) throws HyracksDataException;
+    IPushRuntime[] createPushRuntime(IHyracksTaskContext ctx) throws HyracksDataException;
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/aggreg/NestedPlansAccumulatingAggregatorFactory.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/aggreg/NestedPlansAccumulatingAggregatorFactory.java
index 94af04f..0a578f6 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/aggreg/NestedPlansAccumulatingAggregatorFactory.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/aggreg/NestedPlansAccumulatingAggregatorFactory.java
@@ -168,7 +168,7 @@
         // should enforce protocol
         boolean enforce = ctx.getJobFlags().contains(JobFlag.ENFORCE_CONTRACT);
         for (int i = runtimeFactories.length - 1; i >= 0; i--) {
-            IPushRuntime newRuntime = runtimeFactories[i].createPushRuntime(ctx);
+            IPushRuntime newRuntime = runtimeFactories[i].createPushRuntime(ctx)[0];
             newRuntime = enforce ? EnforcePushRuntime.enforce(newRuntime) : newRuntime;
             start = enforce ? EnforcePushRuntime.enforce(start) : start;
             newRuntime.setOutputFrameWriter(0, start, recordDescriptors[i]);
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/aggreg/NestedPlansRunningAggregatorFactory.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/aggreg/NestedPlansRunningAggregatorFactory.java
index c261df8..75b2fb2 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/aggreg/NestedPlansRunningAggregatorFactory.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/aggreg/NestedPlansRunningAggregatorFactory.java
@@ -149,7 +149,7 @@
         IPushRuntimeFactory[] runtimeFactories = subplan.getRuntimeFactories();
         RecordDescriptor[] recordDescriptors = subplan.getRecordDescriptors();
         for (int i = runtimeFactories.length - 1; i >= 0; i--) {
-            IPushRuntime newRuntime = runtimeFactories[i].createPushRuntime(ctx);
+            IPushRuntime newRuntime = runtimeFactories[i].createPushRuntime(ctx)[0];
             newRuntime = enforce ? EnforcePushRuntime.enforce(newRuntime) : newRuntime;
             start = enforce ? EnforceFrameWriter.enforce(start) : start;
             newRuntime.setOutputFrameWriter(0, start, recordDescriptors[i]);
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/base/AbstractOneInputOneOutputRuntimeFactory.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/base/AbstractOneInputOneOutputRuntimeFactory.java
index 32eff3a..7b3fb46 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/base/AbstractOneInputOneOutputRuntimeFactory.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/base/AbstractOneInputOneOutputRuntimeFactory.java
@@ -34,8 +34,8 @@
     }
 
     @Override
-    public IPushRuntime createPushRuntime(IHyracksTaskContext ctx) throws HyracksDataException {
-        return createOneOutputPushRuntime(ctx);
+    public IPushRuntime[] createPushRuntime(IHyracksTaskContext ctx) throws HyracksDataException {
+        return new IPushRuntime[] { createOneOutputPushRuntime(ctx) };
     }
 
     public abstract AbstractOneInputOneOutputPushRuntime createOneOutputPushRuntime(IHyracksTaskContext ctx)
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/base/SinkRuntimeFactory.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/base/SinkRuntimeFactory.java
index a838557..f0e9406 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/base/SinkRuntimeFactory.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/base/SinkRuntimeFactory.java
@@ -38,8 +38,8 @@
     }
 
     @Override
-    public IPushRuntime createPushRuntime(IHyracksTaskContext ctx) throws HyracksDataException {
-        return new AbstractOneInputSinkPushRuntime() {
+    public IPushRuntime[] createPushRuntime(IHyracksTaskContext ctx) throws HyracksDataException {
+        return new IPushRuntime[] { new AbstractOneInputSinkPushRuntime() {
 
             @Override
             public void open() throws HyracksDataException {
@@ -61,7 +61,6 @@
             public void flush() throws HyracksDataException {
                 // flush() is meaningless for sink operators
             }
-        };
+        } };
     }
-
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/meta/AlgebricksMetaOperatorDescriptor.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/meta/AlgebricksMetaOperatorDescriptor.java
index b4d23fc..07365db 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/meta/AlgebricksMetaOperatorDescriptor.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/meta/AlgebricksMetaOperatorDescriptor.java
@@ -45,11 +45,18 @@
 
     public AlgebricksMetaOperatorDescriptor(IOperatorDescriptorRegistry spec, int inputArity, int outputArity,
             IPushRuntimeFactory[] runtimeFactories, RecordDescriptor[] internalRecordDescriptors) {
+        this(spec, inputArity, outputArity, runtimeFactories, internalRecordDescriptors, null, null);
+    }
+
+    public AlgebricksMetaOperatorDescriptor(IOperatorDescriptorRegistry spec, int inputArity, int outputArity,
+            IPushRuntimeFactory[] runtimeFactories, RecordDescriptor[] internalRecordDescriptors,
+            IPushRuntimeFactory[] outputRuntimeFactories, int[] outputPositions) {
         super(spec, inputArity, outputArity);
         if (outputArity == 1) {
             this.outRecDescs[0] = internalRecordDescriptors[internalRecordDescriptors.length - 1];
         }
-        this.pipeline = new AlgebricksPipeline(runtimeFactories, internalRecordDescriptors);
+        this.pipeline = new AlgebricksPipeline(runtimeFactories, internalRecordDescriptors, outputRuntimeFactories,
+                outputPositions);
     }
 
     public AlgebricksPipeline getPipeline() {
@@ -81,7 +88,7 @@
     private class SourcePushRuntime extends AbstractUnaryOutputSourceOperatorNodePushable {
         private final IHyracksTaskContext ctx;
 
-        public SourcePushRuntime(IHyracksTaskContext ctx) {
+        SourcePushRuntime(IHyracksTaskContext ctx) {
             this.ctx = ctx;
         }
 
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/meta/PipelineAssembler.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/meta/PipelineAssembler.java
index e1081e0..a717794 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/meta/PipelineAssembler.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/meta/PipelineAssembler.java
@@ -18,9 +18,13 @@
  */
 package org.apache.hyracks.algebricks.runtime.operators.meta;
 
+import java.util.HashMap;
+import java.util.Map;
+
 import org.apache.hyracks.algebricks.runtime.base.AlgebricksPipeline;
 import org.apache.hyracks.algebricks.runtime.base.EnforcePushRuntime;
 import org.apache.hyracks.algebricks.runtime.base.IPushRuntime;
+import org.apache.hyracks.algebricks.runtime.base.IPushRuntimeFactory;
 import org.apache.hyracks.api.comm.IFrameWriter;
 import org.apache.hyracks.api.context.IHyracksTaskContext;
 import org.apache.hyracks.api.dataflow.EnforceFrameWriter;
@@ -37,6 +41,7 @@
     private final int inputArity;
     private final int outputArity;
     private final AlgebricksPipeline pipeline;
+    private final Map<IPushRuntimeFactory, IPushRuntime[]> runtimeMap;
 
     public PipelineAssembler(AlgebricksPipeline pipeline, int inputArity, int outputArity,
             RecordDescriptor pipelineInputRecordDescriptor, RecordDescriptor pipelineOutputRecordDescriptor) {
@@ -45,6 +50,7 @@
         this.pipelineOutputRecordDescriptor = pipelineOutputRecordDescriptor;
         this.inputArity = inputArity;
         this.outputArity = outputArity;
+        this.runtimeMap = new HashMap<>();
     }
 
     public IFrameWriter assemblePipeline(IFrameWriter writer, IHyracksTaskContext ctx) throws HyracksDataException {
@@ -52,19 +58,30 @@
         boolean enforce = ctx.getJobFlags().contains(JobFlag.ENFORCE_CONTRACT);
         // plug the operators
         IFrameWriter start = writer;// this.writer;
-        for (int i = pipeline.getRuntimeFactories().length - 1; i >= 0; i--) {
-            IPushRuntime newRuntime = pipeline.getRuntimeFactories()[i].createPushRuntime(ctx);
-            newRuntime = enforce ? EnforcePushRuntime.enforce(newRuntime) : newRuntime;
+        IPushRuntimeFactory[] runtimeFactories = pipeline.getRuntimeFactories();
+        RecordDescriptor[] recordDescriptors = pipeline.getRecordDescriptors();
+        for (int i = runtimeFactories.length - 1; i >= 0; i--) {
             start = enforce ? EnforceFrameWriter.enforce(start) : start;
-            if (i == pipeline.getRuntimeFactories().length - 1) {
-                if (outputArity == 1) {
-                    newRuntime.setOutputFrameWriter(0, start, pipelineOutputRecordDescriptor);
+
+            IPushRuntimeFactory runtimeFactory = runtimeFactories[i];
+            IPushRuntime[] newRuntimes = runtimeFactory.createPushRuntime(ctx);
+            for (int j = 0; j < newRuntimes.length; j++) {
+                if (enforce) {
+                    newRuntimes[j] = EnforcePushRuntime.enforce(newRuntimes[j]);
                 }
-            } else {
-                newRuntime.setOutputFrameWriter(0, start, pipeline.getRecordDescriptors()[i]);
+                if (i == runtimeFactories.length - 1) {
+                    if (outputArity == 1) {
+                        newRuntimes[j].setOutputFrameWriter(0, start, pipelineOutputRecordDescriptor);
+                    }
+                } else {
+                    newRuntimes[j].setOutputFrameWriter(0, start, recordDescriptors[i]);
+                }
             }
+            runtimeMap.put(runtimeFactory, newRuntimes);
+
+            IPushRuntime newRuntime = newRuntimes[0];
             if (i > 0) {
-                newRuntime.setInputRecordDescriptor(0, pipeline.getRecordDescriptors()[i - 1]);
+                newRuntime.setInputRecordDescriptor(0, recordDescriptors[i - 1]);
             } else if (inputArity > 0) {
                 newRuntime.setInputRecordDescriptor(0, pipelineInputRecordDescriptor);
             }
@@ -72,4 +89,8 @@
         }
         return start;
     }
+
+    public IPushRuntime[] getPushRuntime(IPushRuntimeFactory runtimeFactory) {
+        return runtimeMap.get(runtimeFactory);
+    }
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/meta/SubplanRuntimeFactory.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/meta/SubplanRuntimeFactory.java
index 7e04750..159fde7 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/meta/SubplanRuntimeFactory.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/meta/SubplanRuntimeFactory.java
@@ -20,9 +20,11 @@
 
 import java.io.DataOutput;
 import java.nio.ByteBuffer;
+import java.util.List;
 
 import org.apache.hyracks.algebricks.common.exceptions.NotImplementedException;
 import org.apache.hyracks.algebricks.runtime.base.AlgebricksPipeline;
+import org.apache.hyracks.algebricks.runtime.base.IPushRuntime;
 import org.apache.hyracks.algebricks.runtime.base.IPushRuntimeFactory;
 import org.apache.hyracks.algebricks.runtime.operators.base.AbstractOneInputOneOutputOneFramePushRuntime;
 import org.apache.hyracks.algebricks.runtime.operators.base.AbstractOneInputOneOutputPushRuntime;
@@ -41,16 +43,21 @@
 
     private static final long serialVersionUID = 1L;
 
-    private final AlgebricksPipeline pipeline;
+    private final List<AlgebricksPipeline> pipelines;
+
     private final RecordDescriptor inputRecordDesc;
+
+    private final RecordDescriptor outputRecordDesc;
+
     private final IMissingWriterFactory[] missingWriterFactories;
 
-    public SubplanRuntimeFactory(AlgebricksPipeline pipeline, IMissingWriterFactory[] missingWriterFactories,
-            RecordDescriptor inputRecordDesc, int[] projectionList) {
+    public SubplanRuntimeFactory(List<AlgebricksPipeline> pipelines, IMissingWriterFactory[] missingWriterFactories,
+            RecordDescriptor inputRecordDesc, RecordDescriptor outputRecordDesc, int[] projectionList) {
         super(projectionList);
-        this.pipeline = pipeline;
+        this.pipelines = pipelines;
         this.missingWriterFactories = missingWriterFactories;
         this.inputRecordDesc = inputRecordDesc;
+        this.outputRecordDesc = outputRecordDesc;
         if (projectionList != null) {
             throw new NotImplementedException();
         }
@@ -60,8 +67,12 @@
     public String toString() {
         StringBuilder sb = new StringBuilder();
         sb.append("Subplan { \n");
-        for (IPushRuntimeFactory f : pipeline.getRuntimeFactories()) {
-            sb.append("  " + f.toString() + ";\n");
+        for (AlgebricksPipeline pipeline : pipelines) {
+            sb.append('{');
+            for (IPushRuntimeFactory f : pipeline.getRuntimeFactories()) {
+                sb.append("  ").append(f).append(";\n");
+            }
+            sb.append('}');
         }
         sb.append("}");
         return sb.toString();
@@ -70,110 +81,177 @@
     @Override
     public AbstractOneInputOneOutputPushRuntime createOneOutputPushRuntime(final IHyracksTaskContext ctx)
             throws HyracksDataException {
+        return new SubplanPushRuntime(ctx);
+    }
 
-        RecordDescriptor pipelineOutputRecordDescriptor = null;
+    private class SubplanPushRuntime extends AbstractOneInputOneOutputOneFramePushRuntime {
 
-        final PipelineAssembler pa =
-                new PipelineAssembler(pipeline, 1, 1, inputRecordDesc, pipelineOutputRecordDescriptor);
-        final IMissingWriter[] nullWriters = new IMissingWriter[missingWriterFactories.length];
-        for (int i = 0; i < missingWriterFactories.length; i++) {
-            nullWriters[i] = missingWriterFactories[i].createMissingWriter();
+        final IHyracksTaskContext ctx;
+
+        final NestedTupleSourceRuntime[] startOfPipelines;
+
+        boolean first;
+
+        SubplanPushRuntime(IHyracksTaskContext ctx) throws HyracksDataException {
+            this.ctx = ctx;
+            this.first = true;
+
+            IMissingWriter[] missingWriters = new IMissingWriter[missingWriterFactories.length];
+            for (int i = 0; i < missingWriterFactories.length; i++) {
+                missingWriters[i] = missingWriterFactories[i].createMissingWriter();
+            }
+
+            int pipelineCount = pipelines.size();
+            startOfPipelines = new NestedTupleSourceRuntime[pipelineCount];
+            PipelineAssembler[] pipelineAssemblers = new PipelineAssembler[pipelineCount];
+            for (int i = 0; i < pipelineCount; i++) {
+                AlgebricksPipeline pipeline = pipelines.get(i);
+                RecordDescriptor pipelineLastRecordDescriptor =
+                        pipeline.getRecordDescriptors()[pipeline.getRecordDescriptors().length - 1];
+
+                RecordDescriptor outputRecordDescriptor;
+                IFrameWriter outputWriter;
+                if (i == 0) {
+                    // primary pipeline
+                    outputWriter = new TupleOuterProduct(pipelineLastRecordDescriptor, missingWriters);
+                    outputRecordDescriptor = SubplanRuntimeFactory.this.outputRecordDesc;
+                } else {
+                    // secondary pipeline
+                    IPushRuntime outputPushRuntime = linkSecondaryPipeline(pipeline, pipelineAssemblers, i);
+                    if (outputPushRuntime == null) {
+                        throw new IllegalStateException("Invalid pipeline");
+                    }
+                    outputPushRuntime.setInputRecordDescriptor(0, pipelineLastRecordDescriptor);
+                    outputWriter = outputPushRuntime;
+                    outputRecordDescriptor = pipelineLastRecordDescriptor;
+                }
+
+                PipelineAssembler pa = new PipelineAssembler(pipeline, 1, 1, inputRecordDesc, outputRecordDescriptor);
+                startOfPipelines[i] = (NestedTupleSourceRuntime) pa.assemblePipeline(outputWriter, ctx);
+                pipelineAssemblers[i] = pa;
+            }
         }
 
-        return new AbstractOneInputOneOutputOneFramePushRuntime() {
+        IPushRuntime linkSecondaryPipeline(AlgebricksPipeline pipeline, PipelineAssembler[] pipelineAssemblers,
+                int pipelineAssemblersCount) {
+            IPushRuntimeFactory[] outputRuntimeFactories = pipeline.getOutputRuntimeFactories();
+            if (outputRuntimeFactories == null || outputRuntimeFactories.length != 1) {
+                throw new IllegalStateException();
+            }
+            IPushRuntimeFactory outRuntimeFactory = outputRuntimeFactories[0];
+            int outputPosition = pipeline.getOutputPositions()[0];
+            for (int i = 0; i < pipelineAssemblersCount; i++) {
+                IPushRuntime[] p = pipelineAssemblers[i].getPushRuntime(outRuntimeFactory);
+                if (p != null) {
+                    return p[outputPosition];
+                }
+            }
+            return null;
+        }
 
-            /**
-             * Computes the outer product between a given tuple and the frames
-             * passed.
-             */
-            class TupleOuterProduct implements IFrameWriter {
+        @Override
+        public void open() throws HyracksDataException {
+            writer.open();
+            if (first) {
+                first = false;
+                initAccessAppendRef(ctx);
+            }
+        }
 
-                private boolean smthWasWritten = false;
-                private FrameTupleAccessor ta = new FrameTupleAccessor(
-                        pipeline.getRecordDescriptors()[pipeline.getRecordDescriptors().length - 1]);
-                private ArrayTupleBuilder tb = new ArrayTupleBuilder(
-                        nullWriters.length + SubplanRuntimeFactory.this.inputRecordDesc.getFieldCount());
+        @Override
+        public void nextFrame(ByteBuffer buffer) throws HyracksDataException {
+            tAccess.reset(buffer);
+            int nTuple = tAccess.getTupleCount();
+            for (int t = 0; t < nTuple; t++) {
+                tRef.reset(tAccess, t);
 
-                @Override
-                public void open() throws HyracksDataException {
-                    smthWasWritten = false;
+                for (NestedTupleSourceRuntime nts : startOfPipelines) {
+                    nts.writeTuple(buffer, t);
                 }
 
-                @Override
-                public void nextFrame(ByteBuffer buffer) throws HyracksDataException {
-                    ta.reset(buffer);
-                    int nTuple = ta.getTupleCount();
-                    for (int t = 0; t < nTuple; t++) {
-                        appendConcat(tRef.getFrameTupleAccessor(), tRef.getTupleIndex(), ta, t);
+                int n = 0;
+                try {
+                    for (; n < startOfPipelines.length; n++) {
+                        NestedTupleSourceRuntime nts = startOfPipelines[n];
+                        try {
+                            nts.open();
+                        } catch (Exception e) {
+                            nts.fail();
+                            throw e;
+                        }
                     }
-                    smthWasWritten = true;
-                }
-
-                @Override
-                public void close() throws HyracksDataException {
-                    if (!smthWasWritten && !failed) {
-                        // the case when we need to write nulls
-                        appendNullsToTuple();
-                        appendToFrameFromTupleBuilder(tb);
-                    }
-                }
-
-                @Override
-                public void fail() throws HyracksDataException {
-                    // writer.fail() is called by the outer class' writer.fail().
-                }
-
-                private void appendNullsToTuple() throws HyracksDataException {
-                    tb.reset();
-                    int n0 = tRef.getFieldCount();
-                    for (int f = 0; f < n0; f++) {
-                        tb.addField(tRef.getFrameTupleAccessor(), tRef.getTupleIndex(), f);
-                    }
-                    DataOutput dos = tb.getDataOutput();
-                    for (int i = 0; i < nullWriters.length; i++) {
-                        nullWriters[i].writeMissing(dos);
-                        tb.addFieldEndOffset();
+                } finally {
+                    for (int i = n - 1; i >= 0; i--) {
+                        startOfPipelines[i].close();
                     }
                 }
             }
+        }
 
-            IFrameWriter endPipe = new TupleOuterProduct();
+        @Override
+        public void flush() throws HyracksDataException {
+            writer.flush();
+        }
 
-            NestedTupleSourceRuntime startOfPipeline = (NestedTupleSourceRuntime) pa.assemblePipeline(endPipe, ctx);
+        /**
+         * Computes the outer product between a given tuple and the frames
+         * passed.
+         */
+        class TupleOuterProduct implements IFrameWriter {
 
-            boolean first = true;
+            private boolean smthWasWritten;
+            private final FrameTupleAccessor ta;
+            private final ArrayTupleBuilder tb;
+            private final IMissingWriter[] missingWriters;
+
+            private TupleOuterProduct(RecordDescriptor recordDescriptor, IMissingWriter[] missingWriters) {
+                ta = new FrameTupleAccessor(recordDescriptor);
+                tb = new ArrayTupleBuilder(
+                        missingWriters.length + SubplanRuntimeFactory.this.inputRecordDesc.getFieldCount());
+                this.missingWriters = missingWriters;
+            }
 
             @Override
             public void open() throws HyracksDataException {
-                writer.open();
-                if (first) {
-                    first = false;
-                    initAccessAppendRef(ctx);
-                }
+                smthWasWritten = false;
             }
 
             @Override
             public void nextFrame(ByteBuffer buffer) throws HyracksDataException {
-                tAccess.reset(buffer);
-                int nTuple = tAccess.getTupleCount();
+                ta.reset(buffer);
+                int nTuple = ta.getTupleCount();
                 for (int t = 0; t < nTuple; t++) {
-                    tRef.reset(tAccess, t);
-                    startOfPipeline.writeTuple(buffer, t);
-                    try {
-                        startOfPipeline.open();
-                    } catch (Exception e) {
-                        startOfPipeline.fail();
-                        throw e;
-                    } finally {
-                        startOfPipeline.close();
-                    }
+                    appendConcat(tRef.getFrameTupleAccessor(), tRef.getTupleIndex(), ta, t);
+                }
+                smthWasWritten = true;
+            }
+
+            @Override
+            public void close() throws HyracksDataException {
+                if (!smthWasWritten && !failed) {
+                    // the case when we need to write nulls
+                    appendNullsToTuple();
+                    appendToFrameFromTupleBuilder(tb);
                 }
             }
 
             @Override
-            public void flush() throws HyracksDataException {
-                writer.flush();
+            public void fail() throws HyracksDataException {
+                // writer.fail() is called by the outer class' writer.fail().
             }
-        };
+
+            private void appendNullsToTuple() throws HyracksDataException {
+                tb.reset();
+                int n0 = tRef.getFieldCount();
+                for (int f = 0; f < n0; f++) {
+                    tb.addField(tRef.getFrameTupleAccessor(), tRef.getTupleIndex(), f);
+                }
+                DataOutput dos = tb.getDataOutput();
+                for (IMissingWriter missingWriter : missingWriters) {
+                    missingWriter.writeMissing(dos);
+                    tb.addFieldEndOffset();
+                }
+            }
+        }
     }
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/EmptyTupleSourceRuntimeFactory.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/EmptyTupleSourceRuntimeFactory.java
index 3ccceed..67f4a77 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/EmptyTupleSourceRuntimeFactory.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/EmptyTupleSourceRuntimeFactory.java
@@ -40,8 +40,8 @@
     }
 
     @Override
-    public IPushRuntime createPushRuntime(final IHyracksTaskContext ctx) throws HyracksDataException {
-        return new AbstractOneInputSourcePushRuntime() {
+    public IPushRuntime[] createPushRuntime(final IHyracksTaskContext ctx) throws HyracksDataException {
+        return new IPushRuntime[] { new AbstractOneInputSourcePushRuntime() {
 
             private final ArrayTupleBuilder tb = new ArrayTupleBuilder(0);
             private final FrameTupleAppender appender = new FrameTupleAppender(new VSizeFrame(ctx));
@@ -69,6 +69,6 @@
             public void flush() throws HyracksDataException {
                 appender.flush(writer);
             }
-        };
+        } };
     }
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/NestedTupleSourceRuntimeFactory.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/NestedTupleSourceRuntimeFactory.java
index 496679f..8e64092 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/NestedTupleSourceRuntimeFactory.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/NestedTupleSourceRuntimeFactory.java
@@ -39,8 +39,8 @@
     }
 
     @Override
-    public IPushRuntime createPushRuntime(IHyracksTaskContext ctx) throws HyracksDataException {
-        return new NestedTupleSourceRuntime(ctx);
+    public IPushRuntime[] createPushRuntime(IHyracksTaskContext ctx) throws HyracksDataException {
+        return new IPushRuntime[] { new NestedTupleSourceRuntime(ctx) };
     }
 
     public static class NestedTupleSourceRuntime extends AbstractOneInputOneOutputOneFramePushRuntime {
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/PrinterRuntimeFactory.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/PrinterRuntimeFactory.java
index 021784a..8a06ecf 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/PrinterRuntimeFactory.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/PrinterRuntimeFactory.java
@@ -56,9 +56,9 @@
     }
 
     @Override
-    public IPushRuntime createPushRuntime(IHyracksTaskContext ctx) {
+    public IPushRuntime[] createPushRuntime(IHyracksTaskContext ctx) {
         IAWriter w = PrinterBasedWriterFactory.INSTANCE.createWriter(printColumns, System.out, printerFactories,
                 inputRecordDesc);
-        return new SinkWriterRuntime(w, System.out, inputRecordDesc);
+        return new IPushRuntime[] { new SinkWriterRuntime(w, System.out, inputRecordDesc) };
     }
 }
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/SinkWriterRuntimeFactory.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/SinkWriterRuntimeFactory.java
index d52ceee..536a769 100644
--- a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/SinkWriterRuntimeFactory.java
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/std/SinkWriterRuntimeFactory.java
@@ -67,11 +67,11 @@
     }
 
     @Override
-    public IPushRuntime createPushRuntime(IHyracksTaskContext ctx) throws HyracksDataException {
+    public IPushRuntime[] createPushRuntime(IHyracksTaskContext ctx) throws HyracksDataException {
         try {
             PrintStream filePrintStream = new PrintStream(new BufferedOutputStream(new FileOutputStream(outputFile)));
             IAWriter w = writerFactory.createWriter(fields, filePrintStream, printerFactories, inputRecordDesc);
-            return new SinkWriterRuntime(w, filePrintStream, inputRecordDesc, true);
+            return new IPushRuntime[] { new SinkWriterRuntime(w, filePrintStream, inputRecordDesc, true) };
         } catch (IOException e) {
             throw new HyracksDataException(e);
         }
diff --git a/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/union/MicroUnionAllRuntimeFactory.java b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/union/MicroUnionAllRuntimeFactory.java
new file mode 100644
index 0000000..1706e59
--- /dev/null
+++ b/hyracks-fullstack/algebricks/algebricks-runtime/src/main/java/org/apache/hyracks/algebricks/runtime/operators/union/MicroUnionAllRuntimeFactory.java
@@ -0,0 +1,112 @@
+/*
+ * 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.hyracks.algebricks.runtime.operators.union;
+
+import java.nio.ByteBuffer;
+
+import org.apache.commons.lang3.mutable.Mutable;
+import org.apache.commons.lang3.mutable.MutableObject;
+import org.apache.hyracks.algebricks.runtime.base.IPushRuntime;
+import org.apache.hyracks.algebricks.runtime.base.IPushRuntimeFactory;
+import org.apache.hyracks.api.comm.IFrameWriter;
+import org.apache.hyracks.api.context.IHyracksTaskContext;
+import org.apache.hyracks.api.dataflow.value.RecordDescriptor;
+import org.apache.hyracks.api.exceptions.HyracksDataException;
+
+public class MicroUnionAllRuntimeFactory implements IPushRuntimeFactory {
+
+    private static final long serialVersionUID = 1L;
+
+    private final int inputArity;
+
+    public MicroUnionAllRuntimeFactory(int inputArity) {
+        this.inputArity = inputArity;
+    }
+
+    @Override
+    public IPushRuntime[] createPushRuntime(IHyracksTaskContext ctx) {
+        Mutable<Boolean> failedShared = new MutableObject<>(Boolean.FALSE);
+        IPushRuntime[] result = new IPushRuntime[inputArity];
+        for (int i = 0; i < inputArity; i++) {
+            result[i] = new MicroUnionAllPushRuntime(i, failedShared);
+        }
+        return result;
+    }
+
+    @Override
+    public String toString() {
+        return "union-all";
+    }
+
+    private final class MicroUnionAllPushRuntime implements IPushRuntime {
+
+        private final int idx;
+
+        private final Mutable<Boolean> failedShared;
+
+        private IFrameWriter writer;
+
+        MicroUnionAllPushRuntime(int idx, Mutable<Boolean> failedShared) {
+            this.idx = idx;
+            this.failedShared = failedShared;
+        }
+
+        @Override
+        public void setOutputFrameWriter(int index, IFrameWriter writer, RecordDescriptor recordDesc) {
+            if (index != 0) {
+                throw new IllegalArgumentException(String.valueOf(index));
+            }
+            this.writer = writer;
+        }
+
+        @Override
+        public void setInputRecordDescriptor(int index, RecordDescriptor recordDescriptor) {
+            // input is not accessed
+        }
+
+        @Override
+        public void open() throws HyracksDataException {
+            if (idx == 0) {
+                writer.open();
+            }
+        }
+
+        @Override
+        public void nextFrame(ByteBuffer buffer) throws HyracksDataException {
+            writer.nextFrame(buffer);
+        }
+
+        @Override
+        public void fail() throws HyracksDataException {
+            boolean failed = failedShared.getValue();
+            failedShared.setValue(Boolean.TRUE);
+            if (!failed) {
+                writer.fail();
+            }
+        }
+
+        @Override
+        public void close() throws HyracksDataException {
+            if (idx == 0) {
+                writer.close();
+            }
+        }
+    }
+}
diff --git a/hyracks-fullstack/algebricks/algebricks-tests/src/test/java/org/apache/hyracks/algebricks/tests/pushruntime/PushRuntimeTest.java b/hyracks-fullstack/algebricks/algebricks-tests/src/test/java/org/apache/hyracks/algebricks/tests/pushruntime/PushRuntimeTest.java
index 40e2ec6..a7621ec 100644
--- a/hyracks-fullstack/algebricks/algebricks-tests/src/test/java/org/apache/hyracks/algebricks/tests/pushruntime/PushRuntimeTest.java
+++ b/hyracks-fullstack/algebricks/algebricks-tests/src/test/java/org/apache/hyracks/algebricks/tests/pushruntime/PushRuntimeTest.java
@@ -22,6 +22,7 @@
 import java.io.File;
 import java.io.FileReader;
 import java.io.IOException;
+import java.util.Collections;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import org.apache.commons.io.FileUtils;
@@ -439,7 +440,7 @@
         RecordDescriptor aggDesc =
                 new RecordDescriptor(new ISerializerDeserializer[] { IntegerSerializerDeserializer.INSTANCE });
         AlgebricksPipeline pipeline = new AlgebricksPipeline(new IPushRuntimeFactory[] { nts, agg },
-                new RecordDescriptor[] { ntsDesc, aggDesc });
+                new RecordDescriptor[] { ntsDesc, aggDesc }, null, null);
         NestedPlansAccumulatingAggregatorFactory npaaf = new NestedPlansAccumulatingAggregatorFactory(
                 new AlgebricksPipeline[] { pipeline }, new int[] { 3 }, new int[] {});
         RecordDescriptor gbyDesc = new RecordDescriptor(new ISerializerDeserializer[] {
@@ -780,10 +781,10 @@
                 new RecordDescriptor(new ISerializerDeserializer[] { IntegerSerializerDeserializer.INSTANCE });
 
         AlgebricksPipeline pipeline = new AlgebricksPipeline(new IPushRuntimeFactory[] { nts, assign2, project1 },
-                new RecordDescriptor[] { assign1Desc, assign2Desc, project1Desc });
+                new RecordDescriptor[] { assign1Desc, assign2Desc, project1Desc }, null, null);
 
-        SubplanRuntimeFactory subplan = new SubplanRuntimeFactory(pipeline,
-                new IMissingWriterFactory[] { NoopMissingWriterFactory.INSTANCE }, assign1Desc, null);
+        SubplanRuntimeFactory subplan = new SubplanRuntimeFactory(Collections.singletonList(pipeline),
+                new IMissingWriterFactory[] { NoopMissingWriterFactory.INSTANCE }, assign1Desc, null, null);
 
         RecordDescriptor subplanDesc = new RecordDescriptor(new ISerializerDeserializer[] {
                 IntegerSerializerDeserializer.INSTANCE, IntegerSerializerDeserializer.INSTANCE });
@@ -851,7 +852,7 @@
         RecordDescriptor aggDesc =
                 new RecordDescriptor(new ISerializerDeserializer[] { IntegerSerializerDeserializer.INSTANCE });
         AlgebricksPipeline pipeline = new AlgebricksPipeline(new IPushRuntimeFactory[] { nts, agg },
-                new RecordDescriptor[] { ntsDesc, aggDesc });
+                new RecordDescriptor[] { ntsDesc, aggDesc }, null, null);
         NestedPlansAccumulatingAggregatorFactory npaaf = new NestedPlansAccumulatingAggregatorFactory(
                 new AlgebricksPipeline[] { pipeline }, new int[] { 3 }, new int[] {});
         RecordDescriptor gbyDesc = new RecordDescriptor(new ISerializerDeserializer[] {
diff --git a/hyracks-fullstack/hyracks/hyracks-api/src/main/java/org/apache/hyracks/api/job/JobSpecification.java b/hyracks-fullstack/hyracks/hyracks-api/src/main/java/org/apache/hyracks/api/job/JobSpecification.java
index 9f66080..c4c7320 100644
--- a/hyracks-fullstack/hyracks/hyracks-api/src/main/java/org/apache/hyracks/api/job/JobSpecification.java
+++ b/hyracks-fullstack/hyracks/hyracks-api/src/main/java/org/apache/hyracks/api/job/JobSpecification.java
@@ -89,6 +89,8 @@
 
     private transient int connectorIdCounter;
 
+    private transient List<IOperatorDescriptor> metaOps;
+
     // This constructor uses the default frame size. It is for test purposes only.
     // For other use cases, use the one which sets the frame size.
     public JobSpecification() {
@@ -308,6 +310,14 @@
         return requiredClusterCapacity;
     }
 
+    public void setMetaOps(List<IOperatorDescriptor> metaOps) {
+        this.metaOps = metaOps;
+    }
+
+    public List<IOperatorDescriptor> getMetaOps() {
+        return metaOps;
+    }
+
     private <K, V> void insertIntoIndexedMap(Map<K, List<V>> map, K key, int index, V value) {
         List<V> vList = map.computeIfAbsent(key, k -> new ArrayList<>());
         extend(vList, index);