Fixed a bug in EventListener::OnCompactionCompleted().

Summary:
Fixed a bug in EventListener::OnCompactionCompleted() that returns
incorrect list of input / output file names.

Test Plan: Extend existing test in listener_test.cc

Reviewers: sdong, rven, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D38349

1 files changed, 12 insertions, 0 deletions

diff --git a/include/rocksdb/listener.h b/include/rocksdb/listener.h
index be5b96032..7f70d1c8e 100644
--- a/include/rocksdb/listener.h
+++ b/include/rocksdb/listener.h
@@ -45,6 +45,18 @@ struct CompactionJobInfo {
 // actual thread that involves in that specific event.   For example, it
 // is the RocksDB background flush thread that does the actual flush to
 // call EventListener::OnFlushCompleted().
+//
+// [Locking] All EventListener callbacks are designed to be called without
+// the current thread holding any DB mutex. This is to prevent potential
+// deadlock and performance issue when using EventListener callback
+// in a complex way. However, all EventListener call-back functions
+// should not run for an extended period of time before the function
+// returns, otherwise RocksDB may be blocked. For example, it is not
+// suggested to do DB::CompactFiles() (as it may run for a long while)
+// or issue many of DB::Put() (as Put may be blocked in certain cases)
+// in the same thread in the EventListener callback. However, doing
+// DB::CompactFiles() and DB::Put() in a thread other than the
+// EventListener callback thread is considered safe.
 class EventListener {
  public:
   // A call-back function to RocksDB which will be called whenever a