SERVER-48561 Merging unique leaf nodes in the radix tree with the same data should not be a merge conflict

2 files changed, 26 insertions, 3 deletions

diff --git a/src/mongo/db/storage/biggie/store.h b/src/mongo/db/storage/biggie/store.h
index 80da6009cf9..a2f74a29945 100644
--- a/src/mongo/db/storage/biggie/store.h
+++ b/src/mongo/db/storage/biggie/store.h
@@ -1407,9 +1407,13 @@ private:
                     current->_children[key] = other->_children[key];
                 }
             } else if (baseNode && otherNode && baseNode != otherNode) {
-                // If all three are unique and leaf nodes, then it is a merge conflict.
-                if (node->isLeaf() && baseNode->isLeaf() && otherNode->isLeaf())
-                    throw merge_conflict_exception();
+                // If all three are unique and leaf nodes with different data, then it is a merge
+                // conflict.
+                if (node->isLeaf() && baseNode->isLeaf() && otherNode->isLeaf()) {
+                    if (node->_data != baseNode->_data || baseNode->_data != otherNode->_data)
+                        throw merge_conflict_exception();
+                    continue;
+                }
 
                 // If the keys and data are all the exact same, then we can keep recursing.
                 // Otherwise, we manually resolve the differences element by element. The
diff --git a/src/mongo/db/storage/biggie/store_test.cpp b/src/mongo/db/storage/biggie/store_test.cpp
index c49b8411e52..a61c1fe978f 100644
--- a/src/mongo/db/storage/biggie/store_test.cpp
+++ b/src/mongo/db/storage/biggie/store_test.cpp
@@ -1709,6 +1709,25 @@ TEST_F(RadixStoreTest, MergeConflictingInsertions) {
     ASSERT_THROWS(thisStore.merge3(baseStore, otherStore), merge_conflict_exception);
 }
 
+TEST_F(RadixStoreTest, MergeDifferentLeafNodesSameDataTest) {
+    baseStore.insert({"a", "a"});
+    baseStore.insert({"aa", "a"});
+
+    otherStore = baseStore;
+    otherStore.insert({"aaa", "a"});
+    otherStore.erase("aaa");
+
+    thisStore = baseStore;
+    thisStore.insert({"aab", "b"});
+    thisStore.erase("aab");
+
+    thisStore.merge3(baseStore, otherStore);
+
+    expected.insert({"a", "a"});
+    expected.insert({"aa", "a"});
+    ASSERT_TRUE(thisStore == expected);
+}
+
 TEST_F(RadixStoreTest, UpperBoundTest) {
     value_type value1 = std::make_pair("foo", "1");
     value_type value2 = std::make_pair("bar", "2");