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

sync/syncable/on_disk_directory_backing_store.cc

 // Copyright (c) 2012 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/on_disk_directory_backing_store.h"
 
 #include "base/logging.h"
 #include "base/stl_util.h"
 #include "base/metrics/histogram.h"
 #include "sync/syncable/syncable-inl.h"
@@ skipping 19 matching lines @@
       backing_filepath_(backing_filepath) {
   db_->set_exclusive_locking();
   db_->set_page_size(4096);
 }
 
 OnDiskDirectoryBackingStore::~OnDiskDirectoryBackingStore() { }
 
 DirOpenResult OnDiskDirectoryBackingStore::TryLoad(
     Directory::MetahandlesMap* handles_map,
     JournalIndex* delete_journals,
+    MetahandleSet* metahandles_to_purge,
     Directory::KernelLoadInfo* kernel_load_info) {
   DCHECK(CalledOnValidThread());
   if (!db_->is_open()) {
     if (!db_->Open(backing_filepath_))
       return FAILED_OPEN_DATABASE;
   }
 
   if (!InitializeTables())
     return FAILED_OPEN_DATABASE;
 
-  if (!DropDeletedEntries())
-    return FAILED_DATABASE_CORRUPT;
-  if (!LoadEntries(handles_map))
+  if (!LoadEntries(handles_map, metahandles_to_purge))
     return FAILED_DATABASE_CORRUPT;
   if (!LoadDeleteJournals(delete_journals))
     return FAILED_DATABASE_CORRUPT;
   if (!LoadInfo(kernel_load_info))
     return FAILED_DATABASE_CORRUPT;
   if (!VerifyReferenceIntegrity(handles_map))
     return FAILED_DATABASE_CORRUPT;
 
   return OPENED;
 
 }
 
 DirOpenResult OnDiskDirectoryBackingStore::Load(
     Directory::MetahandlesMap* handles_map,
     JournalIndex* delete_journals,
+    MetahandleSet* metahandles_to_purge,
     Directory::KernelLoadInfo* kernel_load_info) {
   DirOpenResult result = TryLoad(handles_map, delete_journals,
-                                 kernel_load_info);
+                                 metahandles_to_purge, kernel_load_info);
   if (result == OPENED) {
     UMA_HISTOGRAM_ENUMERATION(
         "Sync.DirectoryOpenResult", FIRST_TRY_SUCCESS, RESULT_COUNT);
     return OPENED;
   }
 
   ReportFirstTryOpenFailure();
 
   // The fallback: delete the current database and return a fresh one.  We can
   // fetch the user's data from the cloud.
   STLDeleteValues(handles_map);
   STLDeleteElements(delete_journals);
   db_.reset(new sql::Connection);
   // TODO: Manually propagating the default database settings is
   // brittle.  Either have a helper to set these up (or generate a new
   // connection), or add something like Reset() to sql::Connection.
   db_->set_exclusive_locking();
   db_->set_page_size(4096);
   db_->set_histogram_tag("SyncDirectory");
   base::DeleteFile(backing_filepath_, false);
 
-  result = TryLoad(handles_map, delete_journals, kernel_load_info);
+  result = TryLoad(handles_map, delete_journals, metahandles_to_purge,
+                   kernel_load_info);
   if (result == OPENED) {
     UMA_HISTOGRAM_ENUMERATION(
         "Sync.DirectoryOpenResult", SECOND_TRY_SUCCESS, RESULT_COUNT);
   } else {
     UMA_HISTOGRAM_ENUMERATION(
         "Sync.DirectoryOpenResult", SECOND_TRY_FAILURE, RESULT_COUNT);
   }
 
   return result;
 }
 
 void OnDiskDirectoryBackingStore::ReportFirstTryOpenFailure() {
   // In debug builds, the last thing we want is to silently clear the database.
   // It's full of evidence that might help us determine what went wrong.  It
   // might be sqlite's fault, but it could also be a bug in sync.  We crash
   // immediately so a developer can investigate.
   //
   // Developers: If you're not interested in debugging this right now, just move
   // aside the 'Sync Data' directory in your profile.  This is similar to what
   // the code would do if this DCHECK were disabled.
   NOTREACHED() << "Crashing to preserve corrupt sync database";
 }
 
 }  // namespace syncable
 }  // namespace syncer