SERVER-33106 set multiKeyPaths and clear plan cache in onCommit hook

Without this change, if the WriteUnitOfWork aborts, we will set the
multiKeyPaths for the index without actually marking it as multiKey.

1 files changed, 17 insertions, 12 deletions

diff --git a/src/mongo/db/catalog/index_catalog_entry_impl.cpp b/src/mongo/db/catalog/index_catalog_entry_impl.cpp
index cbea2f00a00..46abd0e3170 100644
--- a/src/mongo/db/catalog/index_catalog_entry_impl.cpp
+++ b/src/mongo/db/catalog/index_catalog_entry_impl.cpp
@@ -272,22 +272,27 @@ void IndexCatalogEntryImpl::setMultikey(OperationContext* opCtx,
     // CollectionCatalogEntry::setIndexIsMultikey() requires that we discard the path-level
     // multikey information in order to avoid unintentionally setting path-level multikey
     // information on an index created before 3.4.
-    if (_collection->setIndexIsMultikey(opCtx, _descriptor->indexName(), paths)) {
-        if (_infoCache) {
+    const bool indexMetadataHasChanged =
+        _collection->setIndexIsMultikey(opCtx, _descriptor->indexName(), paths);
+
+    // When the recovery unit commits, update the multikey paths if needed and clear the plan cache
+    // if the index metadata has changed.
+    opCtx->recoveryUnit()->onCommit([this, multikeyPaths, indexMetadataHasChanged] {
+        _isMultikey.store(true);
+
+        if (_indexTracksPathLevelMultikeyInfo) {
+            stdx::lock_guard<stdx::mutex> lk(_indexMultikeyPathsMutex);
+            for (size_t i = 0; i < multikeyPaths.size(); ++i) {
+                _indexMultikeyPaths[i].insert(multikeyPaths[i].begin(), multikeyPaths[i].end());
+            }
+        }
+
+        if (indexMetadataHasChanged && _infoCache) {
             LOG(1) << _ns << ": clearing plan cache - index " << _descriptor->keyPattern()
                    << " set to multi key.";
             _infoCache->clearQueryCache();
         }
-    }
-
-    opCtx->recoveryUnit()->onCommit([this] { _isMultikey.store(true); });
-
-    if (_indexTracksPathLevelMultikeyInfo) {
-        stdx::lock_guard<stdx::mutex> lk(_indexMultikeyPathsMutex);
-        for (size_t i = 0; i < multikeyPaths.size(); ++i) {
-            _indexMultikeyPaths[i].insert(multikeyPaths[i].begin(), multikeyPaths[i].end());
-        }
-    }
+    });
 }
 
 // ----