SERVER-48034 Fix bug in radix store merge3() when the nodes just diff in the data they hold

2 files changed, 19 insertions, 2 deletions

diff --git a/src/mongo/db/storage/biggie/store.h b/src/mongo/db/storage/biggie/store.h
index a09b5b49b63..7ae2087617c 100644
--- a/src/mongo/db/storage/biggie/store.h
+++ b/src/mongo/db/storage/biggie/store.h
@@ -1404,13 +1404,14 @@ private:
                 if (node->isLeaf() && baseNode->isLeaf() && otherNode->isLeaf())
                     throw merge_conflict_exception();
 
-                // If the keys are all the exact same, then we can keep recursing.
+                // 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
                 // structure of compressed radix tries makes it difficult to compare the
                 // trees node by node, hence the reason for resolving these differences
                 // element by element.
                 if (node->_trieKey == baseNode->_trieKey &&
-                    baseNode->_trieKey == otherNode->_trieKey) {
+                    baseNode->_trieKey == otherNode->_trieKey && node->_data == baseNode->_data &&
+                    baseNode->_data == otherNode->_data) {
                     _merge3Helper(node, baseNode, otherNode, context, trieKeyIndex);
                 } else {
                     _mergeResolveConflict(node, baseNode, otherNode);
diff --git a/src/mongo/db/storage/biggie/store_test.cpp b/src/mongo/db/storage/biggie/store_test.cpp
index e75a81bc7c7..14f23d9551c 100644
--- a/src/mongo/db/storage/biggie/store_test.cpp
+++ b/src/mongo/db/storage/biggie/store_test.cpp
@@ -1575,6 +1575,22 @@ TEST_F(RadixStoreTest, MergeInsertionDeletionModification) {
     ASSERT_EQ(itemsVisited, 4);
 }
 
+TEST_F(RadixStoreTest, MergeOnlyDataDifferenceInBranch) {
+    baseStore.insert({"a", ""});
+    baseStore.insert({"aa", ""});
+
+    otherStore = baseStore;
+    otherStore.update({"a", "a"});
+
+    thisStore = baseStore;
+    thisStore.update({"aa", "b"});
+    thisStore.merge3(baseStore, otherStore);
+
+    expected.insert({"a", "a"});
+    expected.insert({"aa", "b"});
+    ASSERT_TRUE(thisStore == expected);
+}
+
 TEST_F(RadixStoreTest, MergeConflictingModifications) {
     value_type value1 = std::make_pair("foo", "1");
     value_type value2 = std::make_pair("foo", "2");