SERVER-21646 limit concurrency of writes to replicated capped collections

This prevents the primary from running significantly faster than secondaries.

(cherry picked from commit f45b7c8e34743ba89407d90ee3392acb0d2be255)

2 files changed, 20 insertions, 7 deletions

diff --git a/src/mongo/db/catalog/collection.cpp b/src/mongo/db/catalog/collection.cpp
index 9b8e9a0726a..936909a4456 100644
--- a/src/mongo/db/catalog/collection.cpp
+++ b/src/mongo/db/catalog/collection.cpp
@@ -44,6 +44,7 @@
 #include "mongo/db/catalog/collection_catalog_entry.h"
 #include "mongo/db/catalog/database_catalog_entry.h"
 #include "mongo/db/catalog/index_create.h"
+#include "mongo/db/global_environment_experiment.h"
 #include "mongo/db/index/index_access_method.h"
 #include "mongo/db/operation_context.h"
 #include "mongo/db/repl/replication_coordinator_global.h"
@@ -92,6 +93,7 @@ Collection::Collection(OperationContext* txn,
       _details(details),
       _recordStore(recordStore),
       _dbce(dbce),
+      _needCappedLock(supportsDocLocking() && _recordStore->isCapped() && _ns.db() != "local"),
       _infoCache(this),
       _indexCatalog(this),
       _cursorManager(fullNS) {
@@ -227,9 +229,12 @@ StatusWith<RecordId> Collection::_insertDocument(OperationContext* txn,
                                                  bool enforceQuota) {
     dassert(txn->lockState()->isCollectionLockedForMode(ns().toString(), MODE_IX));
 
-    // TODO: for now, capped logic lives inside NamespaceDetails, which is hidden
-    //       under the RecordStore, this feels broken since that should be a
-    //       collection access method probably
+    if (_needCappedLock) {
+        // X-lock the metadata resource for this capped collection until the end of the WUOW. This
+        // prevents the primary from executing with more concurrency than secondaries.
+        // See SERVER-21646.
+        Lock::ResourceLock{txn->lockState(), ResourceId(RESOURCE_METADATA, _ns.ns()), MODE_X};
+    }
 
     StatusWith<RecordId> loc = _recordStore->insertRecord(
         txn, docToInsert.objdata(), docToInsert.objsize(), _enforceQuota(enforceQuota));
@@ -296,6 +301,13 @@ StatusWith<RecordId> Collection::updateDocument(OperationContext* txn,
     dassert(txn->lockState()->isCollectionLockedForMode(ns().toString(), MODE_IX));
     invariant(objOld.snapshotId() == txn->recoveryUnit()->getSnapshotId());
 
+    if (_needCappedLock) {
+        // X-lock the metadata resource for this capped collection until the end of the WUOW. This
+        // prevents the primary from executing with more concurrency than secondaries.
+        // See SERVER-21646.
+        Lock::ResourceLock{txn->lockState(), ResourceId(RESOURCE_METADATA, _ns.ns()), MODE_X};
+    }
+
     SnapshotId sid = txn->recoveryUnit()->getSnapshotId();
 
     BSONElement oldId = objOld.value()["_id"];
diff --git a/src/mongo/db/catalog/collection.h b/src/mongo/db/catalog/collection.h
index f09cbd9b79b..d64dd95aef8 100644
--- a/src/mongo/db/catalog/collection.h
+++ b/src/mongo/db/catalog/collection.h
@@ -319,10 +319,11 @@ private:
 
     int _magic;
 
-    NamespaceString _ns;
-    CollectionCatalogEntry* _details;
-    RecordStore* _recordStore;
-    DatabaseCatalogEntry* _dbce;
+    const NamespaceString _ns;
+    CollectionCatalogEntry* const _details;
+    RecordStore* const _recordStore;
+    DatabaseCatalogEntry* const _dbce;
+    const bool _needCappedLock;
     CollectionInfoCache _infoCache;
     IndexCatalog _indexCatalog;