diff --git a/be/src/exec/partitioned-aggregation-node-ir.cc b/be/src/exec/partitioned-aggregation-node-ir.cc
index 9baada1..69d297c 100644
--- a/be/src/exec/partitioned-aggregation-node-ir.cc
+++ b/be/src/exec/partitioned-aggregation-node-ir.cc
@@ -221,7 +221,6 @@
   DCHECK(remaining_capacity != NULL);
   DCHECK_EQ(hash_tbl, partition->hash_tbl.get());
   DCHECK_GE(*remaining_capacity, 0);
-  if (hash_tbl == nullptr) return false; // Hash table was not created - pass through.
   bool found;
   // This is called from ProcessBatchStreaming() so the rows are not aggregated.
   HashTable::Iterator it = hash_tbl->FindBuildRowBucket(ht_ctx, &found);
diff --git a/be/src/exec/partitioned-aggregation-node.cc b/be/src/exec/partitioned-aggregation-node.cc
index 214810f..3824a72 100644
--- a/be/src/exec/partitioned-aggregation-node.cc
+++ b/be/src/exec/partitioned-aggregation-node.cc
@@ -529,12 +529,8 @@
     bool ht_needs_expansion = false;
     for (int i = 0; i < PARTITION_FANOUT; ++i) {
       HashTable* hash_tbl = GetHashTable(i);
-      if (hash_tbl == nullptr) {
-        remaining_capacity[i] = 0;
-      } else {
-        remaining_capacity[i] = hash_tbl->NumInsertsBeforeResize();
-        ht_needs_expansion |= remaining_capacity[i] < child_batch_->num_rows();
-      }
+      remaining_capacity[i] = hash_tbl->NumInsertsBeforeResize();
+      ht_needs_expansion |= remaining_capacity[i] < child_batch_->num_rows();
     }
 
     // Stop expanding hash tables if we're not reducing the input sufficiently. As our
@@ -545,7 +541,7 @@
     if (ht_needs_expansion && ShouldExpandPreaggHashTables()) {
       for (int i = 0; i < PARTITION_FANOUT; ++i) {
         HashTable* ht = GetHashTable(i);
-        if (ht != nullptr && remaining_capacity[i] < child_batch_->num_rows()) {
+        if (remaining_capacity[i] < child_batch_->num_rows()) {
           SCOPED_TIMER(ht_resize_timer_);
           bool resized;
           RETURN_IF_ERROR(
@@ -585,10 +581,8 @@
   int64_t ht_rows = 0;
   for (int i = 0; i < PARTITION_FANOUT; ++i) {
     HashTable* ht = hash_partitions_[i]->hash_tbl.get();
-    if (ht != nullptr) {
-      ht_mem += ht->CurrentMemSize();
-      ht_rows += ht->size();
-    }
+    ht_mem += ht->CurrentMemSize();
+    ht_rows += ht->size();
   }
 
   // Need some rows in tables to have valid statistics.
@@ -728,16 +722,9 @@
   RETURN_IF_ERROR(aggregated_row_stream->Init(parent->id(), true));
   bool got_buffer;
   RETURN_IF_ERROR(aggregated_row_stream->PrepareForWrite(&got_buffer));
-  if (!got_buffer) {
-    stringstream ss;
-    parent->DebugString(2, &ss);
-    DCHECK(parent->is_streaming_preagg_)
-        << "Merge agg should have enough reservation " << parent->id_ << "\n"
-        << parent->buffer_pool_client_.DebugString() << "\n"
-        << ss.str();
-    DiscardAggregatedRowStream();
-  }
-
+  DCHECK(got_buffer) << "Buffer included in reservation " << parent->id_ << "\n"
+                     << parent->buffer_pool_client_.DebugString() << "\n"
+                     << parent->DebugString(2);
   if (!parent->is_streaming_preagg_) {
     unaggregated_row_stream.reset(new BufferedTupleStream(parent->state_,
         parent->child(0)->row_desc(), &parent->buffer_pool_client_,
@@ -830,16 +817,6 @@
   return Status::OK();
 }
 
-void PartitionedAggregationNode::Partition::DiscardAggregatedRowStream() {
-  DCHECK(parent->is_streaming_preagg_);
-  DCHECK(aggregated_row_stream != nullptr);
-  DCHECK_EQ(aggregated_row_stream->num_rows(), 0);
-  if (hash_tbl != nullptr) hash_tbl->Close();
-  hash_tbl.reset();
-  aggregated_row_stream->Close(nullptr, RowBatch::FlushMode::NO_FLUSH_RESOURCES);
-  aggregated_row_stream.reset();
-}
-
 Status PartitionedAggregationNode::Partition::Spill(bool more_aggregate_rows) {
   DCHECK(!parent->is_streaming_preagg_);
   DCHECK(!is_closed);
@@ -1093,6 +1070,12 @@
   }
 }
 
+string PartitionedAggregationNode::DebugString(int indentation_level) const {
+  stringstream ss;
+  DebugString(indentation_level, &ss);
+  return ss.str();
+}
+
 void PartitionedAggregationNode::DebugString(
     int indentation_level, stringstream* out) const {
   *out << string(indentation_level * 2, ' ');
@@ -1142,12 +1125,9 @@
       RETURN_IF_ERROR(partition->InitHashTable(&got_memory));
       // Spill the partition if we cannot create a hash table for a merge aggregation.
       if (UNLIKELY(!got_memory)) {
-        if (is_streaming_preagg_) {
-          partition->DiscardAggregatedRowStream();
-        } else {
-          // If we're repartitioning, we will be writing aggregated rows first.
-          RETURN_IF_ERROR(partition->Spill(level > 0));
-        }
+        DCHECK(!is_streaming_preagg_) << "Preagg reserves enough memory for hash tables";
+        // If we're repartitioning, we will be writing aggregated rows first.
+        RETURN_IF_ERROR(partition->Spill(level > 0));
       }
     }
     hash_tbls_[i] = partition->hash_tbl.get();
diff --git a/be/src/exec/partitioned-aggregation-node.h b/be/src/exec/partitioned-aggregation-node.h
index ade223b..72354cc 100644
--- a/be/src/exec/partitioned-aggregation-node.h
+++ b/be/src/exec/partitioned-aggregation-node.h
@@ -146,6 +146,7 @@
  protected:
   /// Frees local allocations from aggregate_evals_ and agg_fn_evals
   virtual Status QueryMaintenance(RuntimeState* state);
+  virtual std::string DebugString(int indentation_level) const;
   virtual void DebugString(int indentation_level, std::stringstream* out) const;
 
  private:
@@ -394,11 +395,6 @@
     /// if 'more_aggregate_rows' is true or the unaggregated stream otherwise.
     Status Spill(bool more_aggregate_rows) WARN_UNUSED_RESULT;
 
-    /// Discards the aggregated row stream and hash table. Only valid to call if this is
-    /// a streaming preaggregation and the initial memory allocation for hash tables or
-    /// the aggregated stream failed. The aggregated stream must have 0 rows.
-    void DiscardAggregatedRowStream();
-
     bool is_spilled() const { return hash_tbl.get() == NULL; }
 
     PartitionedAggregationNode* parent;
@@ -732,7 +728,10 @@
   int64_t MinReservation() const {
     DCHECK(!grouping_exprs_.empty());
     // Must be kept in sync with AggregationNode.computeNodeResourceProfile() in fe.
-    if (is_streaming_preagg_) return 0; // Need 0 buffers to pass through rows.
+    if (is_streaming_preagg_) {
+      // Reserve at least one buffer and a 64kb hash table per partition.
+      return (resource_profile_.spillable_buffer_size + 64 * 1024) * PARTITION_FANOUT;
+    }
     int num_buffers = PARTITION_FANOUT + 1 + (needs_serialize_ ? 1 : 0);
     // Two of the buffers must fit the maximum row.
     return resource_profile_.spillable_buffer_size * (num_buffers - 2) +
diff --git a/fe/src/main/java/org/apache/impala/planner/AggregationNode.java b/fe/src/main/java/org/apache/impala/planner/AggregationNode.java
index ce725e0..2778a7f 100644
--- a/fe/src/main/java/org/apache/impala/planner/AggregationNode.java
+++ b/fe/src/main/java/org/apache/impala/planner/AggregationNode.java
@@ -304,25 +304,35 @@
     long bufferSize = queryOptions.getDefault_spillable_buffer_size();
     long maxRowBufferSize =
         computeMaxSpillableBufferSize(bufferSize, queryOptions.getMax_row_size());
-    if (aggInfo_.getGroupingExprs().isEmpty() || useStreamingPreagg_) {
+    if (aggInfo_.getGroupingExprs().isEmpty()) {
       perInstanceMinReservation = 0;
     } else {
+      // This is a grouping pre-aggregation or merge aggregation.
       final int PARTITION_FANOUT = 16;
-      long minBuffers = PARTITION_FANOUT + 1 + (aggInfo_.needsSerialize() ? 1 : 0);
       if (perInstanceDataBytes != -1) {
-        long bytesPerBuffer = perInstanceDataBytes / PARTITION_FANOUT;
+        long bytesPerPartition = perInstanceDataBytes / PARTITION_FANOUT;
         // Scale down the buffer size if we think there will be excess free space with the
         // default buffer size, e.g. with small dimension tables.
         bufferSize = Math.min(bufferSize, Math.max(
             queryOptions.getMin_spillable_buffer_size(),
-            BitUtil.roundUpToPowerOf2(bytesPerBuffer)));
+            BitUtil.roundUpToPowerOf2(bytesPerPartition)));
         // Recompute the max row buffer size with the smaller buffer.
         maxRowBufferSize =
             computeMaxSpillableBufferSize(bufferSize, queryOptions.getMax_row_size());
       }
-      // Two of the buffers need to be buffers large enough to hold the maximum-sized row
-      // to serve as input and output buffers while repartitioning.
-      perInstanceMinReservation = bufferSize * (minBuffers - 2) + maxRowBufferSize * 2;
+      if (useStreamingPreagg_) {
+        // We can execute a streaming preagg without any buffers by passing through rows,
+        // but that is a very low performance mode of execution if the aggregation reduces
+        // its input significantly. Instead reserve memory for one buffer and 64kb of hash
+        // tables per partition. We don't need to reserve memory for large rows since they
+        // can be passed through if needed.
+        perInstanceMinReservation = (bufferSize + 64 * 1024) * PARTITION_FANOUT;
+      } else {
+        long minBuffers = PARTITION_FANOUT + 1 + (aggInfo_.needsSerialize() ? 1 : 0);
+        // Two of the buffers need to be buffers large enough to hold the maximum-sized
+        // row to serve as input and output buffers while repartitioning.
+        perInstanceMinReservation = bufferSize * (minBuffers - 2) + maxRowBufferSize * 2;
+      }
     }
 
     nodeResourceProfile_ = new ResourceProfileBuilder()
diff --git a/testdata/workloads/functional-planner/queries/PlannerTest/max-row-size.test b/testdata/workloads/functional-planner/queries/PlannerTest/max-row-size.test
index 0732771..5a0a76c 100644
--- a/testdata/workloads/functional-planner/queries/PlannerTest/max-row-size.test
+++ b/testdata/workloads/functional-planner/queries/PlannerTest/max-row-size.test
@@ -150,7 +150,7 @@
 group by 1, 2
 having count(*) = 1
 ---- DISTRIBUTEDPLAN
-Max Per-Host Resource Reservation: Memory=77.00MB
+Max Per-Host Resource Reservation: Memory=110.00MB
 Per-Host Resource Estimates: Memory=251.12MB
 
 F04:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
@@ -176,11 +176,11 @@
 |  tuple-ids=2 row-size=33B cardinality=4690314
 |
 F02:PLAN FRAGMENT [HASH(l_orderkey)] hosts=3 instances=3
-Per-Host Resources: mem-estimate=85.12MB mem-reservation=31.00MB
+Per-Host Resources: mem-estimate=85.12MB mem-reservation=64.00MB
 03:AGGREGATE [STREAMING]
 |  output: count(*)
 |  group by: l_orderkey, o_orderstatus
-|  mem-estimate=54.12MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=54.12MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=2 row-size=33B cardinality=4690314
 |
 02:HASH JOIN [INNER JOIN, PARTITIONED]
@@ -224,7 +224,7 @@
 select distinct *
 from tpch_parquet.lineitem
 ---- DISTRIBUTEDPLAN
-Max Per-Host Resource Reservation: Memory=46.00MB
+Max Per-Host Resource Reservation: Memory=79.00MB
 Per-Host Resource Estimates: Memory=3.31GB
 
 F02:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
@@ -248,10 +248,10 @@
 |  tuple-ids=1 row-size=263B cardinality=6001215
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=3 instances=3
-Per-Host Resources: mem-estimate=1.69GB mem-reservation=0B
+Per-Host Resources: mem-estimate=1.69GB mem-reservation=33.00MB
 01:AGGREGATE [STREAMING]
 |  group by: tpch_parquet.lineitem.l_orderkey, tpch_parquet.lineitem.l_partkey, tpch_parquet.lineitem.l_suppkey, tpch_parquet.lineitem.l_linenumber, tpch_parquet.lineitem.l_quantity, tpch_parquet.lineitem.l_extendedprice, tpch_parquet.lineitem.l_discount, tpch_parquet.lineitem.l_tax, tpch_parquet.lineitem.l_returnflag, tpch_parquet.lineitem.l_linestatus, tpch_parquet.lineitem.l_shipdate, tpch_parquet.lineitem.l_commitdate, tpch_parquet.lineitem.l_receiptdate, tpch_parquet.lineitem.l_shipinstruct, tpch_parquet.lineitem.l_shipmode, tpch_parquet.lineitem.l_comment
-|  mem-estimate=1.62GB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=1.62GB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=1 row-size=263B cardinality=6001215
 |
 00:SCAN HDFS [tpch_parquet.lineitem, RANDOM]
@@ -268,7 +268,7 @@
 from tpch_parquet.lineitem
 group by 1, 2
 ---- DISTRIBUTEDPLAN
-Max Per-Host Resource Reservation: Memory=48.00MB
+Max Per-Host Resource Reservation: Memory=81.00MB
 Per-Host Resource Estimates: Memory=482.91MB
 
 F02:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
@@ -293,11 +293,11 @@
 |  tuple-ids=1 row-size=32B cardinality=6001215
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=3 instances=3
-Per-Host Resources: mem-estimate=281.46MB mem-reservation=0B
+Per-Host Resources: mem-estimate=281.46MB mem-reservation=33.00MB
 01:AGGREGATE [STREAMING]
 |  output: group_concat(l_linestatus, ',')
 |  group by: l_orderkey, l_partkey
-|  mem-estimate=201.46MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=201.46MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=1 row-size=32B cardinality=6001215
 |
 00:SCAN HDFS [tpch_parquet.lineitem, RANDOM]
diff --git a/testdata/workloads/functional-planner/queries/PlannerTest/mt-dop-validation.test b/testdata/workloads/functional-planner/queries/PlannerTest/mt-dop-validation.test
index 98239a7..9f80785 100644
--- a/testdata/workloads/functional-planner/queries/PlannerTest/mt-dop-validation.test
+++ b/testdata/workloads/functional-planner/queries/PlannerTest/mt-dop-validation.test
@@ -95,11 +95,11 @@
 |  tuple-ids=1 row-size=16B cardinality=unavailable
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=3 instances=9
-Per-Host Resources: mem-estimate=432.00MB mem-reservation=0B
+Per-Host Resources: mem-estimate=432.00MB mem-reservation=99.00MB
 01:AGGREGATE [STREAMING]
 |  output: count(int_col)
 |  group by: bigint_col
-|  mem-estimate=128.00MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=128.00MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=1 row-size=16B cardinality=unavailable
 |
 00:SCAN HDFS [functional_parquet.alltypes, RANDOM]
diff --git a/testdata/workloads/functional-planner/queries/PlannerTest/resource-requirements.test b/testdata/workloads/functional-planner/queries/PlannerTest/resource-requirements.test
index b9afdf9..90035c1 100644
--- a/testdata/workloads/functional-planner/queries/PlannerTest/resource-requirements.test
+++ b/testdata/workloads/functional-planner/queries/PlannerTest/resource-requirements.test
@@ -375,8 +375,8 @@
    mem-estimate=80.00MB mem-reservation=0B
    tuple-ids=0 row-size=8B cardinality=6001215
 ---- DISTRIBUTEDPLAN
-Max Per-Host Resource Reservation: Memory=8.50MB
-Per-Host Resource Estimates: Memory=116.24MB
+Max Per-Host Resource Reservation: Memory=41.50MB
+Per-Host Resource Estimates: Memory=123.00MB
 
 F02:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
 |  Per-Host Resources: mem-estimate=0B mem-reservation=0B
@@ -400,11 +400,11 @@
 |  tuple-ids=1 row-size=16B cardinality=1563438
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=3 instances=3
-Per-Host Resources: mem-estimate=106.24MB mem-reservation=0B
+Per-Host Resources: mem-estimate=113.00MB mem-reservation=33.00MB
 01:AGGREGATE [STREAMING]
 |  output: count(*)
 |  group by: l_orderkey
-|  mem-estimate=26.24MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=33.00MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=1 row-size=16B cardinality=1563438
 |
 00:SCAN HDFS [tpch_parquet.lineitem, RANDOM]
@@ -415,8 +415,8 @@
    mem-estimate=80.00MB mem-reservation=0B
    tuple-ids=0 row-size=8B cardinality=6001215
 ---- PARALLELPLANS
-Max Per-Host Resource Reservation: Memory=9.50MB
-Per-Host Resource Estimates: Memory=232.48MB
+Max Per-Host Resource Reservation: Memory=75.50MB
+Per-Host Resource Estimates: Memory=246.00MB
 
 F02:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
 |  Per-Host Resources: mem-estimate=0B mem-reservation=0B
@@ -440,11 +440,11 @@
 |  tuple-ids=1 row-size=16B cardinality=1563438
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=3 instances=6
-Per-Host Resources: mem-estimate=212.48MB mem-reservation=0B
+Per-Host Resources: mem-estimate=226.00MB mem-reservation=66.00MB
 01:AGGREGATE [STREAMING]
 |  output: count(*)
 |  group by: l_orderkey
-|  mem-estimate=26.24MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=33.00MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=1 row-size=16B cardinality=1563438
 |
 00:SCAN HDFS [tpch_parquet.lineitem, RANDOM]
@@ -1548,7 +1548,7 @@
    mem-estimate=80.00MB mem-reservation=0B
    tuple-ids=0 row-size=78B cardinality=600122
 ---- DISTRIBUTEDPLAN
-Max Per-Host Resource Reservation: Memory=38.75MB
+Max Per-Host Resource Reservation: Memory=71.75MB
 Per-Host Resource Estimates: Memory=344.33MB
 
 F09:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
@@ -1643,10 +1643,10 @@
 |  tuple-ids=2 row-size=70B cardinality=575772
 |
 F02:PLAN FRAGMENT [HASH(l_orderkey)] hosts=3 instances=3
-Per-Host Resources: mem-estimate=47.33MB mem-reservation=4.75MB
+Per-Host Resources: mem-estimate=47.33MB mem-reservation=37.75MB
 04:AGGREGATE [STREAMING]
 |  group by: l_orderkey, l_partkey, l_suppkey, l_linenumber, l_comment
-|  mem-estimate=42.58MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=42.58MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=2 row-size=70B cardinality=575772
 |
 03:HASH JOIN [INNER JOIN, PARTITIONED]
@@ -1688,7 +1688,7 @@
    mem-estimate=80.00MB mem-reservation=0B
    tuple-ids=0 row-size=78B cardinality=600122
 ---- PARALLELPLANS
-Max Per-Host Resource Reservation: Memory=73.75MB
+Max Per-Host Resource Reservation: Memory=139.75MB
 Per-Host Resource Estimates: Memory=684.91MB
 
 F09:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
@@ -1799,10 +1799,10 @@
 |  tuple-ids=2 row-size=70B cardinality=575772
 |
 F02:PLAN FRAGMENT [HASH(l_orderkey)] hosts=3 instances=6
-Per-Host Resources: mem-estimate=90.91MB mem-reservation=5.75MB
+Per-Host Resources: mem-estimate=90.91MB mem-reservation=71.75MB
 04:AGGREGATE [STREAMING]
 |  group by: l_orderkey, l_partkey, l_suppkey, l_linenumber, l_comment
-|  mem-estimate=42.58MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=42.58MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=2 row-size=70B cardinality=575772
 |
 03:HASH JOIN [INNER JOIN, PARTITIONED]
@@ -1968,7 +1968,7 @@
    mem-estimate=88.00MB mem-reservation=0B
    tuple-ids=2 row-size=16B cardinality=6001215
 ---- DISTRIBUTEDPLAN
-Max Per-Host Resource Reservation: Memory=84.12MB
+Max Per-Host Resource Reservation: Memory=150.12MB
 Per-Host Resource Estimates: Memory=511.55MB
 
 F07:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
@@ -2000,11 +2000,11 @@
 |  tuple-ids=6 row-size=100B cardinality=575772
 |
 F02:PLAN FRAGMENT [HASH(l_orderkey)] hosts=3 instances=3
-Per-Host Resources: mem-estimate=115.78MB mem-reservation=50.12MB
+Per-Host Resources: mem-estimate=115.78MB mem-reservation=83.12MB
 08:AGGREGATE [STREAMING]
 |  output: sum(l_quantity)
 |  group by: c_name, c_custkey, o_orderkey, o_orderdate, o_totalprice
-|  mem-estimate=60.40MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=60.40MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=6 row-size=100B cardinality=575772
 |
 07:HASH JOIN [LEFT SEMI JOIN, PARTITIONED]
@@ -2025,11 +2025,11 @@
 |  |  tuple-ids=4 row-size=24B cardinality=1563438
 |  |
 |  F04:PLAN FRAGMENT [RANDOM] hosts=3 instances=3
-|  Per-Host Resources: mem-estimate=127.36MB mem-reservation=0B
+|  Per-Host Resources: mem-estimate=127.36MB mem-reservation=33.00MB
 |  04:AGGREGATE [STREAMING]
 |  |  output: sum(l_quantity)
 |  |  group by: l_orderkey
-|  |  mem-estimate=39.36MB mem-reservation=0B spill-buffer=2.00MB
+|  |  mem-estimate=39.36MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  |  tuple-ids=4 row-size=24B cardinality=1563438
 |  |
 |  03:SCAN HDFS [tpch.lineitem, RANDOM]
@@ -2098,7 +2098,7 @@
    mem-estimate=88.00MB mem-reservation=0B
    tuple-ids=2 row-size=16B cardinality=6001215
 ---- PARALLELPLANS
-Max Per-Host Resource Reservation: Memory=122.88MB
+Max Per-Host Resource Reservation: Memory=254.88MB
 Per-Host Resource Estimates: Memory=967.22MB
 
 F07:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
@@ -2130,11 +2130,11 @@
 |  tuple-ids=6 row-size=100B cardinality=575772
 |
 F02:PLAN FRAGMENT [HASH(l_orderkey)] hosts=3 instances=6
-Per-Host Resources: mem-estimate=175.68MB mem-reservation=54.88MB
+Per-Host Resources: mem-estimate=175.68MB mem-reservation=120.88MB
 08:AGGREGATE [STREAMING]
 |  output: sum(l_quantity)
 |  group by: c_name, c_custkey, o_orderkey, o_orderdate, o_totalprice
-|  mem-estimate=60.40MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=60.40MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=6 row-size=100B cardinality=575772
 |
 07:HASH JOIN [LEFT SEMI JOIN, PARTITIONED]
@@ -2163,11 +2163,11 @@
 |  |  tuple-ids=4 row-size=24B cardinality=1563438
 |  |
 |  F04:PLAN FRAGMENT [RANDOM] hosts=3 instances=6
-|  Per-Host Resources: mem-estimate=254.73MB mem-reservation=0B
+|  Per-Host Resources: mem-estimate=254.73MB mem-reservation=66.00MB
 |  04:AGGREGATE [STREAMING]
 |  |  output: sum(l_quantity)
 |  |  group by: l_orderkey
-|  |  mem-estimate=39.36MB mem-reservation=0B spill-buffer=2.00MB
+|  |  mem-estimate=39.36MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  |  tuple-ids=4 row-size=24B cardinality=1563438
 |  |
 |  03:SCAN HDFS [tpch.lineitem, RANDOM]
@@ -2452,7 +2452,7 @@
    mem-estimate=88.00MB mem-reservation=0B
    tuple-ids=0 row-size=66B cardinality=150000
 ---- DISTRIBUTEDPLAN
-Max Per-Host Resource Reservation: Memory=69.94MB
+Max Per-Host Resource Reservation: Memory=102.94MB
 Per-Host Resource Estimates: Memory=473.94MB
 WARNING: The following tables are missing relevant table and/or column statistics.
 tpch_nested_parquet.customer
@@ -2478,10 +2478,10 @@
 |  tuple-ids=6 row-size=58B cardinality=1500000
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=3 instances=3
-Per-Host Resources: mem-estimate=345.94MB mem-reservation=35.94MB
+Per-Host Resources: mem-estimate=345.94MB mem-reservation=68.94MB
 09:AGGREGATE [STREAMING]
 |  group by: c_name, o1.o_orderkey, o2.o_orderstatus
-|  mem-estimate=128.00MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=128.00MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=6 row-size=58B cardinality=1500000
 |
 01:SUBPLAN
@@ -2531,7 +2531,7 @@
    mem-estimate=88.00MB mem-reservation=0B
    tuple-ids=0 row-size=66B cardinality=150000
 ---- PARALLELPLANS
-Max Per-Host Resource Reservation: Memory=139.88MB
+Max Per-Host Resource Reservation: Memory=205.88MB
 Per-Host Resource Estimates: Memory=947.88MB
 WARNING: The following tables are missing relevant table and/or column statistics.
 tpch_nested_parquet.customer
@@ -2557,10 +2557,10 @@
 |  tuple-ids=6 row-size=58B cardinality=1500000
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=3 instances=6
-Per-Host Resources: mem-estimate=691.88MB mem-reservation=71.88MB
+Per-Host Resources: mem-estimate=691.88MB mem-reservation=137.88MB
 09:AGGREGATE [STREAMING]
 |  group by: c_name, o1.o_orderkey, o2.o_orderstatus
-|  mem-estimate=128.00MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=128.00MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=6 row-size=58B cardinality=1500000
 |
 01:SUBPLAN
diff --git a/testdata/workloads/functional-planner/queries/PlannerTest/spillable-buffer-sizing.test b/testdata/workloads/functional-planner/queries/PlannerTest/spillable-buffer-sizing.test
index 340c3ec..115a8bd 100644
--- a/testdata/workloads/functional-planner/queries/PlannerTest/spillable-buffer-sizing.test
+++ b/testdata/workloads/functional-planner/queries/PlannerTest/spillable-buffer-sizing.test
@@ -516,7 +516,7 @@
 from tpch_parquet.customer
 group by c_nationkey
 ---- DISTRIBUTEDPLAN
-Max Per-Host Resource Reservation: Memory=1.94MB
+Max Per-Host Resource Reservation: Memory=3.94MB
 Per-Host Resource Estimates: Memory=44.00MB
 
 F02:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
@@ -541,11 +541,11 @@
 |  tuple-ids=1 row-size=10B cardinality=25
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=1 instances=1
-Per-Host Resources: mem-estimate=34.00MB mem-reservation=0B
+Per-Host Resources: mem-estimate=34.00MB mem-reservation=2.00MB
 01:AGGREGATE [STREAMING]
 |  output: avg(c_acctbal)
 |  group by: c_nationkey
-|  mem-estimate=10.00MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=10.00MB mem-reservation=2.00MB spill-buffer=64.00KB
 |  tuple-ids=1 row-size=10B cardinality=25
 |
 00:SCAN HDFS [tpch_parquet.customer, RANDOM]
@@ -556,7 +556,7 @@
    mem-estimate=24.00MB mem-reservation=0B
    tuple-ids=0 row-size=10B cardinality=150000
 ---- PARALLELPLANS
-Max Per-Host Resource Reservation: Memory=3.88MB
+Max Per-Host Resource Reservation: Memory=7.88MB
 Per-Host Resource Estimates: Memory=88.00MB
 
 F02:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
@@ -581,11 +581,11 @@
 |  tuple-ids=1 row-size=10B cardinality=25
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=1 instances=2
-Per-Host Resources: mem-estimate=68.00MB mem-reservation=0B
+Per-Host Resources: mem-estimate=68.00MB mem-reservation=4.00MB
 01:AGGREGATE [STREAMING]
 |  output: avg(c_acctbal)
 |  group by: c_nationkey
-|  mem-estimate=10.00MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=10.00MB mem-reservation=2.00MB spill-buffer=64.00KB
 |  tuple-ids=1 row-size=10B cardinality=25
 |
 00:SCAN HDFS [tpch_parquet.customer, RANDOM]
@@ -603,7 +603,7 @@
 group by 1, 2
 having count(*) = 1
 ---- DISTRIBUTEDPLAN
-Max Per-Host Resource Reservation: Memory=51.00MB
+Max Per-Host Resource Reservation: Memory=84.00MB
 Per-Host Resource Estimates: Memory=225.12MB
 
 F04:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
@@ -629,11 +629,11 @@
 |  tuple-ids=2 row-size=33B cardinality=4690314
 |
 F02:PLAN FRAGMENT [HASH(l_orderkey)] hosts=3 instances=3
-Per-Host Resources: mem-estimate=71.12MB mem-reservation=17.00MB
+Per-Host Resources: mem-estimate=71.12MB mem-reservation=50.00MB
 03:AGGREGATE [STREAMING]
 |  output: count(*)
 |  group by: l_orderkey, o_orderstatus
-|  mem-estimate=54.12MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=54.12MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=2 row-size=33B cardinality=4690314
 |
 02:HASH JOIN [INNER JOIN, PARTITIONED]
@@ -672,8 +672,8 @@
    mem-estimate=80.00MB mem-reservation=0B
    tuple-ids=0 row-size=8B cardinality=6001215
 ---- PARALLELPLANS
-Max Per-Host Resource Reservation: Memory=51.00MB
-Per-Host Resource Estimates: Memory=345.12MB
+Max Per-Host Resource Reservation: Memory=117.00MB
+Per-Host Resource Estimates: Memory=357.00MB
 
 F04:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
 |  Per-Host Resources: mem-estimate=0B mem-reservation=0B
@@ -698,11 +698,11 @@
 |  tuple-ids=2 row-size=33B cardinality=4690314
 |
 F02:PLAN FRAGMENT [HASH(l_orderkey)] hosts=3 instances=6
-Per-Host Resources: mem-estimate=71.12MB mem-reservation=17.00MB
+Per-Host Resources: mem-estimate=83.00MB mem-reservation=83.00MB
 03:AGGREGATE [STREAMING]
 |  output: count(*)
 |  group by: l_orderkey, o_orderstatus
-|  mem-estimate=27.06MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=33.00MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=2 row-size=33B cardinality=4690314
 |
 02:HASH JOIN [INNER JOIN, PARTITIONED]
@@ -753,7 +753,7 @@
 select distinct *
 from tpch_parquet.lineitem
 ---- DISTRIBUTEDPLAN
-Max Per-Host Resource Reservation: Memory=34.00MB
+Max Per-Host Resource Reservation: Memory=67.00MB
 Per-Host Resource Estimates: Memory=3.31GB
 
 F02:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
@@ -777,10 +777,10 @@
 |  tuple-ids=1 row-size=263B cardinality=6001215
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=3 instances=3
-Per-Host Resources: mem-estimate=1.69GB mem-reservation=0B
+Per-Host Resources: mem-estimate=1.69GB mem-reservation=33.00MB
 01:AGGREGATE [STREAMING]
 |  group by: tpch_parquet.lineitem.l_orderkey, tpch_parquet.lineitem.l_partkey, tpch_parquet.lineitem.l_suppkey, tpch_parquet.lineitem.l_linenumber, tpch_parquet.lineitem.l_quantity, tpch_parquet.lineitem.l_extendedprice, tpch_parquet.lineitem.l_discount, tpch_parquet.lineitem.l_tax, tpch_parquet.lineitem.l_returnflag, tpch_parquet.lineitem.l_linestatus, tpch_parquet.lineitem.l_shipdate, tpch_parquet.lineitem.l_commitdate, tpch_parquet.lineitem.l_receiptdate, tpch_parquet.lineitem.l_shipinstruct, tpch_parquet.lineitem.l_shipmode, tpch_parquet.lineitem.l_comment
-|  mem-estimate=1.62GB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=1.62GB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=1 row-size=263B cardinality=6001215
 |
 00:SCAN HDFS [tpch_parquet.lineitem, RANDOM]
@@ -791,7 +791,7 @@
    mem-estimate=80.00MB mem-reservation=0B
    tuple-ids=0 row-size=263B cardinality=6001215
 ---- PARALLELPLANS
-Max Per-Host Resource Reservation: Memory=68.00MB
+Max Per-Host Resource Reservation: Memory=134.00MB
 Per-Host Resource Estimates: Memory=6.62GB
 
 F02:PLAN FRAGMENT [UNPARTITIONED] hosts=1 instances=1
@@ -815,10 +815,10 @@
 |  tuple-ids=1 row-size=263B cardinality=6001215
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=3 instances=6
-Per-Host Resources: mem-estimate=3.39GB mem-reservation=0B
+Per-Host Resources: mem-estimate=3.39GB mem-reservation=66.00MB
 01:AGGREGATE [STREAMING]
 |  group by: tpch_parquet.lineitem.l_orderkey, tpch_parquet.lineitem.l_partkey, tpch_parquet.lineitem.l_suppkey, tpch_parquet.lineitem.l_linenumber, tpch_parquet.lineitem.l_quantity, tpch_parquet.lineitem.l_extendedprice, tpch_parquet.lineitem.l_discount, tpch_parquet.lineitem.l_tax, tpch_parquet.lineitem.l_returnflag, tpch_parquet.lineitem.l_linestatus, tpch_parquet.lineitem.l_shipdate, tpch_parquet.lineitem.l_commitdate, tpch_parquet.lineitem.l_receiptdate, tpch_parquet.lineitem.l_shipinstruct, tpch_parquet.lineitem.l_shipmode, tpch_parquet.lineitem.l_comment
-|  mem-estimate=1.62GB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=1.62GB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=1 row-size=263B cardinality=6001215
 |
 00:SCAN HDFS [tpch_parquet.lineitem, RANDOM]
@@ -834,7 +834,7 @@
 from functional_parquet.alltypestiny
 group by string_col
 ---- DISTRIBUTEDPLAN
-Max Per-Host Resource Reservation: Memory=34.00MB
+Max Per-Host Resource Reservation: Memory=67.00MB
 Per-Host Resource Estimates: Memory=272.00MB
 WARNING: The following tables are missing relevant table and/or column statistics.
 functional_parquet.alltypestiny
@@ -861,11 +861,11 @@
 |  tuple-ids=1 row-size=24B cardinality=unavailable
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=3 instances=3
-Per-Host Resources: mem-estimate=144.00MB mem-reservation=0B
+Per-Host Resources: mem-estimate=144.00MB mem-reservation=33.00MB
 01:AGGREGATE [STREAMING]
 |  output: count(*)
 |  group by: string_col
-|  mem-estimate=128.00MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=128.00MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=1 row-size=24B cardinality=unavailable
 |
 00:SCAN HDFS [functional_parquet.alltypestiny, RANDOM]
@@ -876,7 +876,7 @@
    mem-estimate=16.00MB mem-reservation=0B
    tuple-ids=0 row-size=16B cardinality=unavailable
 ---- PARALLELPLANS
-Max Per-Host Resource Reservation: Memory=68.00MB
+Max Per-Host Resource Reservation: Memory=134.00MB
 Per-Host Resource Estimates: Memory=544.00MB
 WARNING: The following tables are missing relevant table and/or column statistics.
 functional_parquet.alltypestiny
@@ -903,11 +903,11 @@
 |  tuple-ids=1 row-size=24B cardinality=unavailable
 |
 F00:PLAN FRAGMENT [RANDOM] hosts=3 instances=6
-Per-Host Resources: mem-estimate=288.00MB mem-reservation=0B
+Per-Host Resources: mem-estimate=288.00MB mem-reservation=66.00MB
 01:AGGREGATE [STREAMING]
 |  output: count(*)
 |  group by: string_col
-|  mem-estimate=128.00MB mem-reservation=0B spill-buffer=2.00MB
+|  mem-estimate=128.00MB mem-reservation=33.00MB spill-buffer=2.00MB
 |  tuple-ids=1 row-size=24B cardinality=unavailable
 |
 00:SCAN HDFS [functional_parquet.alltypestiny, RANDOM]
diff --git a/testdata/workloads/functional-query/queries/QueryTest/spilling-aggs.test b/testdata/workloads/functional-query/queries/QueryTest/spilling-aggs.test
index b7345f2..05552d2 100644
--- a/testdata/workloads/functional-query/queries/QueryTest/spilling-aggs.test
+++ b/testdata/workloads/functional-query/queries/QueryTest/spilling-aggs.test
@@ -168,9 +168,10 @@
 ====
 ---- QUERY
 # Test aggregation with minimum required reservation to exercise IMPALA-2708.
-# Merge aggregation requires 17 buffers. The buffer size is 256k for this test.
+# Merge aggregation requires 17 buffers and preaggregation requires 16 buffers
+# plus 1mb of hash tables. The buffer size is 256k for this test.
 set max_row_size=256k;
-set buffer_pool_limit=4352k;
+set buffer_pool_limit=9472k;
 select count(*)
 from (select distinct * from orders) t
 ---- TYPES