Fix issue #921

Summary:
See a bug report here: https://github.com/facebook/rocksdb/issues/921
The fix is to not check the shared/ directory if share_table_files is false. We could also check FileExists() before GetChildren(), but that will add extra latency when Env is Hdfs :(

Test Plan: added a unit test

Reviewers: rven, sdong, IslamAbdelRahman, yhchiang, anthony

Reviewed By: anthony

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D52593

utilities/backupable/backupable_db.cc

@@ -1344,6 +1344,7 @@ Status BackupEngineImpl::GarbageCollect() {
   assert(!read_only_);
   Log(options_.info_log, "Starting garbage collection");
 
+  if (options_.share_table_files) {
     // delete obsolete shared files
     std::vector<std::string> shared_children;
     {
@@ -1367,6 +1368,7 @@ Status BackupEngineImpl::GarbageCollect() {
         backuped_file_infos_.erase(rel_fname);
       }
     }
+  }
 
   // delete obsolete private files
   std::vector<std::string> private_children;

utilities/backupable/backupable_db_test.cc

@@ -1313,6 +1313,16 @@ TEST_F(BackupableDBTest, EnvFailures) {
     delete backup_engine;
   }
 }
+
+// see https://github.com/facebook/rocksdb/issues/921
+TEST_F(BackupableDBTest, Issue921Test) {
+  BackupEngine* backup_engine;
+  backupable_options_->share_table_files = false;
+  backupable_options_->backup_dir += "/new_dir";
+
+  ASSERT_OK(BackupEngine::Open(env_, *backupable_options_, &backup_engine));
+}
+
 }  // anon namespace
 
 } //  namespace rocksdb