diff --git a/dbms/src/Storages/DeltaMerge/DeltaMergeStore.cpp b/dbms/src/Storages/DeltaMerge/DeltaMergeStore.cpp
index 09f290e311c..73ad22d6d1f 100644
--- a/dbms/src/Storages/DeltaMerge/DeltaMergeStore.cpp
+++ b/dbms/src/Storages/DeltaMerge/DeltaMergeStore.cpp
@@ -1060,6 +1060,13 @@ std::optional<DM::RowKeyRange> DeltaMergeStore::mergeDeltaBySegment(const Contex
             segment = segment_it->second;
         }
 
+        if (!segment->flushCache(*dm_context))
+        {
+            // If the flush failed, it means there are parallel updates to the segment in the background.
+            // In this case, we try again.
+            continue;
+        }
+
         const auto new_segment = segmentMergeDelta(*dm_context, segment, run_thread);
         if (new_segment)
         {
diff --git a/dbms/src/Storages/DeltaMerge/tests/gtest_dm_delta_merge_store.cpp b/dbms/src/Storages/DeltaMerge/tests/gtest_dm_delta_merge_store.cpp
index d46e1b7aa36..b7913c44a2c 100644
--- a/dbms/src/Storages/DeltaMerge/tests/gtest_dm_delta_merge_store.cpp
+++ b/dbms/src/Storages/DeltaMerge/tests/gtest_dm_delta_merge_store.cpp
@@ -3762,6 +3762,55 @@ try
 CATCH
 
 
+// Verify that unflushed data will also be compacted.
+TEST_P(DeltaMergeStoreMergeDeltaBySegmentTest, Flush)
+try
+{
+    {
+        // Write data to first 3 segments and flush.
+        auto newly_written_rows = helper->rows_by_segments[0] + helper->rows_by_segments[1] + helper->rows_by_segments[2];
+        Block block = DMTestEnv::prepareSimpleWriteBlock(0, newly_written_rows, false, pk_type, 5 /* new tso */);
+        store->write(*db_context, db_context->getSettingsRef(), block);
+        store->flushCache(dm_context, RowKeyRange::newAll(store->isCommonHandle(), store->getRowKeyColumnSize()));
+
+        helper->expected_delta_rows[0] += helper->rows_by_segments[0];
+        helper->expected_delta_rows[1] += helper->rows_by_segments[1];
+        helper->expected_delta_rows[2] += helper->rows_by_segments[2];
+        helper->verifyExpectedRowsForAllSegments();
+
+        auto segment1 = std::next(store->segments.begin())->second;
+        ASSERT_EQ(segment1->getDelta()->getUnsavedRows(), 0);
+    }
+    {
+        // Write new data to segment[1] without flush.
+        auto newly_written_rows = helper->rows_by_segments[1];
+        Block block = DMTestEnv::prepareSimpleWriteBlock(helper->rows_by_segments[0], helper->rows_by_segments[0] + newly_written_rows, false, pk_type, 10 /* new tso */);
+        store->write(*db_context, db_context->getSettingsRef(), block);
+
+        helper->expected_delta_rows[1] += helper->rows_by_segments[1];
+        helper->verifyExpectedRowsForAllSegments();
+
+        auto segment1 = std::next(store->segments.begin())->second;
+        ASSERT_GT(segment1->getDelta()->getUnsavedRows(), 0);
+    }
+    {
+        auto segment1 = std::next(store->segments.begin())->second;
+        auto result = store->mergeDeltaBySegment(*db_context, segment1->getRowKeyRange().start, DeltaMergeStore::TaskRunThread::Foreground);
+        ASSERT_NE(result, std::nullopt);
+
+        segment1 = std::next(store->segments.begin())->second;
+        ASSERT_EQ(*result, segment1->getRowKeyRange());
+
+        helper->expected_stable_rows[1] += helper->expected_delta_rows[1];
+        helper->expected_delta_rows[1] = 0;
+        helper->verifyExpectedRowsForAllSegments();
+
+        ASSERT_EQ(segment1->getDelta()->getUnsavedRows(), 0);
+    }
+}
+CATCH
+
+
 } // namespace tests
 } // namespace DM
 } // namespace DB