SERVER-121533 Fix MaxKey range inclusion for migration_destination_manager (#51012)

GitOrigin-RevId: 9c14094e37cb0470cbb5abe293a0919792ded2a0

jstests/sharding/chunk_migration_maxkey_boundary.js

@@ -202,4 +202,33 @@ function assertMigrationComplete(dbName, ns, coll, shard0DB, expectedCount) {
     st.s.getDB(dbName).coll.drop();
 }
 
+// Test 8: Recipient pre-cloning check detects MaxKey orphans with wider-than-shard-key index.
+// checkForExistingDocumentsInRange must extend bounds to the index width so that a MaxKey
+// document already present on the recipient is detected even when the index is wider than
+// the shard key.
+{
+    const {dbName, ns, coll, shard0DB} = setupCollection("recipient_wider_idx", {x: 1});
+    assert.commandWorked(coll.createIndex({x: 1, y: 1}));
+    assert.commandWorked(coll.dropIndex({x: 1}));
+
+    assert.commandWorked(coll.insert({_id: "normal", x: 5}));
+
+    // Directly insert a MaxKey orphan on shard1 (bypassing mongos to simulate an orphan from
+    // a prior buggy migration that left it behind). The wider index {x:1, y:1} means the scan
+    // must use extendRangeBound to pad bounds to match the index width.
+    assert.commandWorked(st.shard1.getDB(dbName).coll.insert({_id: "orphan_maxkey", x: MaxKey(), y: 42}));
+
+    // Migrate the chunk [MinKey, MaxKey) from shard0 to shard1. The recipient's pre-cloning
+    // check should detect the orphaned MaxKey document and abort the migration. Without the
+    // extendRangeBound fix, the wider index scan would use {x: MaxKey, y: MinKey} as the
+    // upper bound, missing the orphan at {x: MaxKey, y: 42}.
+    const result = st.s.adminCommand({moveChunk: ns, find: {x: 0}, to: st.shard1.shardName, _waitForDelete: true});
+
+    assert.commandFailed(result);
+
+    // Clean up the orphan directly on shard1.
+    assert.commandWorked(st.shard1.getDB(dbName).coll.remove({_id: "orphan_maxkey"}));
+    coll.drop();
+}
+
 st.stop();

src/mongo/db/s/migration_destination_manager.cpp

@@ -232,7 +232,7 @@ std::string stateToString(MigrationDestinationManager::State state) {
  * Checks if an upsert of a remote document will override a local document with the same _id but in
  * a different range on this shard. Must be in WriteContext to avoid races and DBHelper errors.
  *
- * TODO: Could optimize this check out if sharding on _id.
+ * TODO SERVER-123300: Could optimize this check out if sharding on _id.
  */
 bool willOverrideLocalId(OperationContext* opCtx,
                          const NamespaceString& nss,
@@ -2234,13 +2234,22 @@ boost::optional<BSONObj> MigrationDestinationManager::checkForExistingDocumentsI
                           << " on collection " << nss.toStringForErrorMsg(),
             shardKeyIdx);
 
-    // Use InternalPlanner to scan the shard key index within the range.
+    // Extend bounds to match the index width and strip field names for the index scan.
+    // When the range max is the global max (all fields MaxKey), use makeUpperInclusive=true
+    // so trailing fields are padded with MaxKey instead of MinKey, and use inclusive upper
+    // bound so the scan detects documents whose shard key is exactly MaxKey. See SERVER-121533.
+    const KeyPattern kp(shardKeyIdx->keyPattern());
+    const bool isMaxGlobal = kp.isGlobalMax(max);
+    const auto extendedMin = Helpers::toKeyFormat(kp.extendRangeBound(min, false));
+    const auto extendedMax = Helpers::toKeyFormat(kp.extendRangeBound(max, isMaxGlobal));
+    const auto boundInclusion = isMaxGlobal ? BoundInclusion::kIncludeBothStartAndEndKeys
+                                            : BoundInclusion::kIncludeStartKeyOnly;
     auto exec = InternalPlanner::shardKeyIndexScan(opCtx,
                                                    collection,
                                                    *shardKeyIdx,
-                                                   min,
-                                                   max,
-                                                   BoundInclusion::kIncludeStartKeyOnly,
+                                                   extendedMin,
+                                                   extendedMax,
+                                                   boundInclusion,
                                                    PlanYieldPolicy::YieldPolicy::YIELD_AUTO,
                                                    InternalPlanner::FORWARD);