diff --git a/velox/experimental/wave/common/tests/BlockTest.cu b/velox/experimental/wave/common/tests/BlockTest.cu
index eab1173a0f40..ade413839d93 100644
--- a/velox/experimental/wave/common/tests/BlockTest.cu
+++ b/velox/experimental/wave/common/tests/BlockTest.cu
@@ -502,7 +502,11 @@ UPDATE_CASE(updateSum1NoSync, testSumNoSync, 0);
 UPDATE_CASE(updateSum1Mtx, testSumMtx, 0);
 UPDATE_CASE(updateSum1MtxCoalesce, testSumMtxCoalesce, 0);
 UPDATE_CASE(updateSum1Atomic, testSumAtomic, 0);
-UPDATE_CASE(updateSum1AtomicCoalesce, testSumAtomicCoalesce, 0);
+UPDATE_CASE(updateSum1AtomicCoalesceShfl, testSumAtomicCoalesceShfl, 0);
+UPDATE_CASE(
+    updateSum1AtomicCoalesceShmem,
+    testSumAtomicCoalesceShmem,
+    run.blockSize * sizeof(int64_t));
 UPDATE_CASE(updateSum1Exch, testSumExch, sizeof(ProbeShared));
 UPDATE_CASE(updateSum1Order, testSumOrder, 0);
 
@@ -662,7 +666,8 @@ REGISTER_KERNEL("partitionShorts", partitionShortsKernel);
 REGISTER_KERNEL("hashTest", hashTestKernel);
 REGISTER_KERNEL("allocatorTest", allocatorTestKernel);
 REGISTER_KERNEL("sum1atm", updateSum1AtomicKernel);
-REGISTER_KERNEL("sum1atmCoa", updateSum1AtomicCoalesceKernel);
+REGISTER_KERNEL("sum1atmCoaShfl", updateSum1AtomicCoalesceShflKernel);
+REGISTER_KERNEL("sum1atmCoaShmem", updateSum1AtomicCoalesceShmemKernel);
 REGISTER_KERNEL("sum1Exch", updateSum1ExchKernel);
 REGISTER_KERNEL("sum1Part", updateSum1PartKernel);
 REGISTER_KERNEL("partSum", update1PartitionKernel);
diff --git a/velox/experimental/wave/common/tests/BlockTest.h b/velox/experimental/wave/common/tests/BlockTest.h
index 2c79469113d0..5218537141a3 100644
--- a/velox/experimental/wave/common/tests/BlockTest.h
+++ b/velox/experimental/wave/common/tests/BlockTest.h
@@ -148,7 +148,8 @@ class BlockTestStream : public Stream {
   void updateSum1Atomic(TestingRow* rows, HashRun& run);
   void updateSum1Exch(TestingRow* rows, HashRun& run);
   void updateSum1NoSync(TestingRow* rows, HashRun& run);
-  void updateSum1AtomicCoalesce(TestingRow* rows, HashRun& run);
+  void updateSum1AtomicCoalesceShfl(TestingRow* rows, HashRun& run);
+  void updateSum1AtomicCoalesceShmem(TestingRow* rows, HashRun& run);
   void updateSum1Part(TestingRow* rows, HashRun& run);
   void updateSum1Mtx(TestingRow* rows, HashRun& run);
   void updateSum1MtxCoalesce(TestingRow* rows, HashRun& run);
diff --git a/velox/experimental/wave/common/tests/HashTableTest.cpp b/velox/experimental/wave/common/tests/HashTableTest.cpp
index 0e5662911411..bae0fd4667dc 100644
--- a/velox/experimental/wave/common/tests/HashTableTest.cpp
+++ b/velox/experimental/wave/common/tests/HashTableTest.cpp
@@ -145,11 +145,15 @@ class HashTableTest : public testing::Test {
       case HashTestCase::kUpdateSum1:
         UPDATE_CASE("sum1Atm", updateSum1Atomic, true, 0);
         UPDATE_CASE("sum1NoSync", updateSum1NoSync, false, 0);
-        UPDATE_CASE("sum1AtmCoa", updateSum1AtomicCoalesce, true, 1);
+        UPDATE_CASE("sum1AtmCoaShfl", updateSum1AtomicCoalesceShfl, true, 1);
+        UPDATE_CASE("sum1AtmCoaShmem", updateSum1AtomicCoalesceShmem, true, 1);
         UPDATE_CASE("sum1Mtx", updateSum1Mtx, true, 1);
         UPDATE_CASE("sum1MtxCoa", updateSum1MtxCoalesce, true, 0);
         UPDATE_CASE("sum1Part", updateSum1Part, true, 0);
-        UPDATE_CASE("sum1Order", updateSum1Order, true, 0);
+        // Commenting out Order and Exch functions as they are too slow.
+        // (for case when only 1 distinct element).
+
+        // UPDATE_CASE("sum1Order", updateSum1Order, true, 0);
         // UPDATE_CASE("sum1Exch", updateSum1Exch, false, 0);
 
         break;
@@ -354,18 +358,28 @@ TEST_F(HashTableTest, update) {
   {
     HashRun run;
     run.testCase = HashTestCase::kUpdateSum1;
-    updateTestCase(1000, 2000000, run);
+    updateTestCase(10000000, 2000000, run);
   }
   {
     HashRun run;
     run.testCase = HashTestCase::kUpdateSum1;
-    updateTestCase(10000000, 2000000, run);
+    updateTestCase(100000, 2000000, run);
+  }
+  {
+    HashRun run;
+    run.testCase = HashTestCase::kUpdateSum1;
+    updateTestCase(1000, 2000000, run);
   }
   {
     HashRun run;
     run.testCase = HashTestCase::kUpdateSum1;
     updateTestCase(10, 2000000, run);
   }
+  {
+    HashRun run;
+    run.testCase = HashTestCase::kUpdateSum1;
+    updateTestCase(1, 2000000, run);
+  }
 }
 
 TEST_F(HashTableTest, groupBy) {
diff --git a/velox/experimental/wave/common/tests/Updates.cuh b/velox/experimental/wave/common/tests/Updates.cuh
index e25b2c918be8..fd0aa491e291 100644
--- a/velox/experimental/wave/common/tests/Updates.cuh
+++ b/velox/experimental/wave/common/tests/Updates.cuh
@@ -102,7 +102,47 @@ void __device__ testSumAtomic(TestingRow* rows, HashProbe* probe) {
   }
 }
 
-void __device__ testSumAtomicCoalesce(TestingRow* rows, HashProbe* probe) {
+void __device__ testSumAtomicCoalesceShmem(TestingRow* rows, HashProbe* probe) {
+  constexpr int32_t kWarpThreads = 32;
+  auto keys = reinterpret_cast<int64_t**>(probe->keys);
+  auto indices = keys[0];
+  auto deltas = keys[1];
+  int32_t base = probe->numRowsPerThread * blockDim.x * blockIdx.x;
+  int32_t lane = cub::LaneId();
+  int32_t end = base + probe->numRows[blockIdx.x];
+  extern __shared__ char smem[];
+
+  int64_t* totals = (int64_t*)smem;
+
+  for (auto count = base; count < end; count += blockDim.x) {
+    auto i = threadIdx.x + count;
+
+    if (i < end) {
+      totals[threadIdx.x] = 0;
+      __syncwarp();
+      uint32_t laneMask = count + kWarpThreads <= end
+          ? 0xffffffff
+          : lowMask<uint32_t>(end - count);
+      auto index = indices[i];
+      auto delta = deltas[i];
+      uint32_t allPeers = __match_any_sync(laneMask, index);
+      int32_t leader = __ffs(allPeers) - 1;
+      atomicAdd(
+          (unsigned long long*)&totals
+              [(threadIdx.x & (~(kWarpThreads - 1))) | leader],
+          (unsigned long long)delta);
+      __syncwarp();
+      if (lane == leader) {
+        auto* row = &rows[index];
+        atomicAdd(
+            (unsigned long long*)&row->count,
+            (unsigned long long)totals[threadIdx.x]);
+      }
+    }
+  }
+}
+
+void __device__ testSumAtomicCoalesceShfl(TestingRow* rows, HashProbe* probe) {
   constexpr int32_t kWarpThreads = 32;
   auto keys = reinterpret_cast<int64_t**>(probe->keys);
   auto indices = keys[0];