Fixed two bugs on logging file deletion.

Summary:
This patch fixes the following two bugs on logging file deletion.

1.  Previously, file deletion failure was only logged in INFO_LEVEL.
    This patch changes it to ERROR_LEVEL and does some code clean.

2.  EventLogger previously will always generate the same log on
    table file deletion even when file deletion is not successful.
    Now the resulting status of file deletion will also be logged.

Test Plan: make all check

Reviewers: sdong, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D38817

db/db_impl.cc

@@ -686,30 +686,36 @@ void DBImpl::PurgeObsoleteFiles(const JobContext& state) {
       // evict from cache
       TableCache::Evict(table_cache_.get(), number);
       fname = TableFileName(db_options_.db_paths, number, path_id);
-      event_logger_.Log() << "job" << state.job_id << "event"
-                          << "table_file_deletion"
-                          << "file_number" << number;
     } else {
       fname = ((type == kLogFile) ?
           db_options_.wal_dir : dbname_) + "/" + to_delete;
     }
 
-#ifdef ROCKSDB_LITE
-    Status s = env_->DeleteFile(fname);
-    Log(InfoLogLevel::DEBUG_LEVEL, db_options_.info_log,
-        "[JOB %d] Delete %s type=%d #%" PRIu64 " -- %s\n", state.job_id,
-        fname.c_str(), type, number, s.ToString().c_str());
-#else   // not ROCKSDB_LITE
+#ifndef ROCKSDB_LITE
     if (type == kLogFile && (db_options_.WAL_ttl_seconds > 0 ||
-                             db_options_.WAL_size_limit_MB > 0)) {
+                              db_options_.WAL_size_limit_MB > 0)) {
       wal_manager_.ArchiveWALFile(fname, number);
-    } else {
-      Status s = env_->DeleteFile(fname);
+      continue;
+    }
+#endif  // !ROCKSDB_LITE
+    auto file_deletion_status = env_->DeleteFile(fname);
+    if (file_deletion_status.ok()) {
       Log(InfoLogLevel::DEBUG_LEVEL, db_options_.info_log,
           "[JOB %d] Delete %s type=%d #%" PRIu64 " -- %s\n", state.job_id,
-          fname.c_str(), type, number, s.ToString().c_str());
+          fname.c_str(), type, number,
+          file_deletion_status.ToString().c_str());
+    } else {
+      Log(InfoLogLevel::ERROR_LEVEL, db_options_.info_log,
+          "[JOB %d] Failed to delete %s type=%d #%" PRIu64 " -- %s\n",
+          state.job_id, fname.c_str(), type, number,
+          file_deletion_status.ToString().c_str());
+    }
+    if (type == kTableFile) {
+      event_logger_.Log() << "job" << state.job_id << "event"
+                          << "table_file_deletion"
+                          << "file_number" << number
+                          << "status" << file_deletion_status.ToString();
     }
-#endif  // ROCKSDB_LITE
   }
 
   // Delete old info log files.