Bug 1072773: Add a preference for enabling SQLite's synchronous=FULL mode in IndexedDB. r=bent

dom/indexedDB/ActorsParent.cpp

@@ -2206,6 +2206,14 @@ SetDefaultPragmas(mozIStorageConnection* aConnection)
     return rv;
   }
 
+  if (IndexedDatabaseManager::FullSynchronous()) {
+    rv = aConnection->ExecuteSimpleSQL(
+                             NS_LITERAL_CSTRING("PRAGMA synchronous = FULL;"));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
   return NS_OK;
 }
 

dom/indexedDB/IndexedDatabaseManager.cpp

@@ -212,6 +212,7 @@ IndexedDatabaseManager::~IndexedDatabaseManager()
 }
 
 bool IndexedDatabaseManager::sIsMainProcess = false;
+bool IndexedDatabaseManager::sFullSynchronousMode = false;
 mozilla::Atomic<bool> IndexedDatabaseManager::sLowDiskSpaceMode(false);
 
 // static
@@ -299,6 +300,14 @@ IndexedDatabaseManager::Init()
   Preferences::RegisterCallbackAndCall(TestingPrefChangedCallback,
                                        kTestingPref);
 
+  // By default IndexedDB uses SQLite with PRAGMA synchronous = NORMAL. This
+  // guarantees (unlike synchronous = OFF) atomicity and consistency, but not
+  // necessarily durability in situations such as power loss. This preference
+  // allows enabling PRAGMA synchronous = FULL on SQLite, which does guarantee
+  // durability, but with an extra fsync() and the corresponding performance
+  // hit.
+  sFullSynchronousMode = Preferences::GetBool("dom.indexedDB.fullSynchronous");
+
   return NS_OK;
 }
 
@@ -502,6 +511,16 @@ IndexedDatabaseManager::InTestingMode()
   return gTestingMode;
 }
 
+// static
+bool
+IndexedDatabaseManager::FullSynchronous()
+{
+  MOZ_ASSERT(gDBManager,
+             "FullSynchronous() called before indexedDB has been initialized!");
+
+  return sFullSynchronousMode;
+}
+
 already_AddRefed<FileManager>
 IndexedDatabaseManager::GetFileManager(PersistenceType aPersistenceType,
                                        const nsACString& aOrigin,

dom/indexedDB/IndexedDatabaseManager.h

@@ -80,6 +80,9 @@ public:
   static bool
   InTestingMode();
 
+  static bool
+  FullSynchronous();
+
   already_AddRefed<FileManager>
   GetFileManager(PersistenceType aPersistenceType,
                  const nsACString& aOrigin,
@@ -162,6 +165,7 @@ private:
   mozilla::Mutex mFileMutex;
 
   static bool sIsMainProcess;
+  static bool sFullSynchronousMode;
   static mozilla::Atomic<bool> sLowDiskSpaceMode;
 };