SERVER-48141 Fix crash in radix store merge3 when merging trees sharing branches not in base

2 files changed, 19 insertions, 1 deletions

diff --git a/src/mongo/db/storage/biggie/store.h b/src/mongo/db/storage/biggie/store.h
index 6798c7aafb0..72e6a639d6f 100644
--- a/src/mongo/db/storage/biggie/store.h
+++ b/src/mongo/db/storage/biggie/store.h
@@ -936,7 +936,9 @@ private:
             }
             depth++;
 
-            if (depth == key.size()) {
+            // Return node if entire trieKey matches.
+            if (depth == key.size() &&
+                (key.size() - initialDepthOffset) == _root->_trieKey.size()) {
                 return _root.get();
             }
         }
diff --git a/src/mongo/db/storage/biggie/store_test.cpp b/src/mongo/db/storage/biggie/store_test.cpp
index 79fbc3de6ed..849df0d4c26 100644
--- a/src/mongo/db/storage/biggie/store_test.cpp
+++ b/src/mongo/db/storage/biggie/store_test.cpp
@@ -1597,6 +1597,22 @@ TEST_F(RadixStoreTest, MergeOnlyDataDifferenceInBranch) {
     ASSERT_TRUE(thisStore == expected);
 }
 
+TEST_F(RadixStoreTest, MergeSharedSubKey) {
+    otherStore = baseStore;
+
+    otherStore.insert({"aaa", "a"});
+    otherStore.insert({"aaab", "b"});
+
+    thisStore = baseStore;
+    thisStore.insert({"aaaa", "a"});
+    thisStore.merge3(baseStore, otherStore);
+
+    expected.insert({"aaa", "a"});
+    expected.insert({"aaaa", "a"});
+    expected.insert({"aaab", "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");