Invoke OnTableFileCreated for empty SSTs (#4307)

Summary:
The API comment on `OnTableFileCreationStarted` (b6280d01f9/include/rocksdb/listener.h (L331-L333)) led users to believe a call to `OnTableFileCreationStarted` will always be matched with a call to `OnTableFileCreated`. However, we were skipping the `OnTableFileCreated` call in one case: no error happens but also no file is generated since there's no data.

This PR adds the call to `OnTableFileCreated` for that case. The filename will be "(nil)" and the size will be zero.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4307

Differential Revision: D9485201

Pulled By: ajkr

fbshipit-source-id: 2f077ec7913f128487aae2624c69a50762394df6

HISTORY.md

@@ -1,6 +1,8 @@
 # Rocksdb Change Log
 ## Unreleased
 ### Public API Change
+* `OnTableFileCreated` will now be called for empty files generated during compaction. In that case, `TableFileCreationInfo::file_path` will be "(nil)" and `TableFileCreationInfo::file_size` will be zero.
+
 ### New Features
 ### Bug Fixes
 

db/compaction_job.cc

@@ -1308,9 +1308,7 @@ Status CompactionJob::FinishCompactionOutputFile(
     // VersionEdit.
     assert(!sub_compact->outputs.empty());
     sub_compact->outputs.pop_back();
-    sub_compact->builder.reset();
-    sub_compact->current_output_file_size = 0;
-    return s;
+    meta = nullptr;
   }
 
   if (s.ok() && (current_entries > 0 || tp.num_range_deletions > 0)) {

tools/db_stress.cc

@@ -1221,7 +1221,9 @@ class DbStressListener : public EventListener {
                    const std::vector<ColumnFamilyDescriptor>& column_families)
       : db_name_(db_name), db_paths_(db_paths),
         column_families_(column_families) {}
-  virtual ~DbStressListener() {}
+  virtual ~DbStressListener() {
+    assert(num_pending_file_creations_ == 0);
+  }
 #ifndef ROCKSDB_LITE
   virtual void OnFlushCompleted(DB* /*db*/, const FlushJobInfo& info) override {
     assert(IsValidColumnFamilyName(info.cf_name));
@@ -1246,16 +1248,23 @@ class DbStressListener : public EventListener {
         std::chrono::microseconds(Random::GetTLSInstance()->Uniform(5000)));
   }
 
+  virtual void OnTableFileCreationStarted(
+      const TableFileCreationBriefInfo& /*info*/) {
+    ++num_pending_file_creations_;
+  }
   virtual void OnTableFileCreated(const TableFileCreationInfo& info) override {
     assert(info.db_name == db_name_);
     assert(IsValidColumnFamilyName(info.cf_name));
+    if (info.file_size) {
       VerifyFilePath(info.file_path);
+    }
     assert(info.job_id > 0 || FLAGS_compact_files_one_in > 0);
     if (info.status.ok() && info.file_size > 0) {
       assert(info.table_properties.data_size > 0);
       assert(info.table_properties.raw_key_size > 0);
       assert(info.table_properties.num_entries > 0);
     }
+    --num_pending_file_creations_;
   }
 
  protected:
@@ -1328,6 +1337,7 @@ class DbStressListener : public EventListener {
   std::string db_name_;
   std::vector<DbPath> db_paths_;
   std::vector<ColumnFamilyDescriptor> column_families_;
+  std::atomic<int> num_pending_file_creations_;
 };
 
 }  // namespace