Sync: Avoid 3 passes over SyncDarta DB when loading the directory from the disk

sync/syncable/directory.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "sync/syncable/directory.h"
 
 #include <algorithm>
 #include <iterator>
 
 #include "base/base64.h"
@@ skipping 59 matching lines @@
     : kernel_info_status(KERNEL_SHARE_INFO_INVALID) {
 }
 
 Directory::SaveChangesSnapshot::~SaveChangesSnapshot() {
   STLDeleteElements(&dirty_metas);
   STLDeleteElements(&delete_journals);
 }
 
 Directory::Kernel::Kernel(
     const std::string& name,
-    const KernelLoadInfo& info, DirectoryChangeDelegate* delegate,
+    const KernelLoadInfo& info,
+    DirectoryChangeDelegate* delegate,
     const WeakHandle<TransactionObserver>& transaction_observer)
     : next_write_transaction_id(0),
       name(name),
       info_status(Directory::KERNEL_SHARE_INFO_VALID),
       persisted_info(info.kernel_info),
       cache_guid(info.cache_guid),
       next_metahandle(info.max_metahandle + 1),
       delegate(delegate),
       transaction_observer(transaction_observer) {
   DCHECK(delegate);
@@ skipping 80 matching lines @@
     DirectoryChangeDelegate* delegate,
     const WeakHandle<TransactionObserver>&
         transaction_observer) {
   KernelLoadInfo info;
   // Temporary indices before kernel_ initialized in case Load fails. We 0(1)
   // swap these later.
   Directory::MetahandlesMap tmp_handles_map;
 
   // Avoids mem leaks on failure.  Harmlessly deletes the empty hash map after
   // the swap in the success case.
-  STLValueDeleter<Directory::MetahandlesMap> deleter(&tmp_handles_map);
+  STLValueDeleter<MetahandlesMap> deleter(&tmp_handles_map);
 
   JournalIndex delete_journals;
+  MetahandleSet metahandles_to_purge;
 
-  DirOpenResult result =
-      store_->Load(&tmp_handles_map, &delete_journals, &info);
+  DirOpenResult result = store_->Load(&tmp_handles_map, &delete_journals,
+                                      &metahandles_to_purge, &info);
   if (OPENED != result)
     return result;
 
   kernel_ = new Kernel(name, info, delegate, transaction_observer);
   delete_journal_.reset(new DeleteJournal(&delete_journals));
   InitializeIndices(&tmp_handles_map);
 
   // Write back the share info to reserve some space in 'next_id'.  This will
   // prevent local ID reuse in the case of an early crash.  See the comments in
   // TakeSnapshotForSaveChanges() or crbug.com/142987 for more information.
   kernel_->info_status = KERNEL_SHARE_INFO_DIRTY;
+
+  kernel_->metahandles_to_purge.swap(metahandles_to_purge);
   if (!SaveChanges())
     return FAILED_INITIAL_WRITE;
 
   return OPENED;
 }
 
 DeleteJournal* Directory::delete_journal() {
   DCHECK(delete_journal_.get());
   return delete_journal_.get();
 }
@@ skipping 1337 matching lines @@
   // TODO(maniscalco): Eliminate redundant metadata storage (bug 415203).
   std::set_difference(not_on_server_id_set.begin(),
                       not_on_server_id_set.end(),
                       on_server_id_set.begin(),
                       on_server_id_set.end(),
                       std::inserter(*id_set, id_set->end()));
 }
 
 }  // namespace syncable
 }  // namespace syncer