Fix ticker stat for number files closed (#4703)

Summary:
We haven't been populating `NO_FILE_CLOSES` since v1.5.8 even though it was never marked as deprecated. Start populating it again. Conveniently `DeleteTableReader` has an unused `void*` argument that we can use...

Blame: 63f216ee0a

Closes #4700.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4703

Differential Revision: D13146769

Pulled By: ajkr

fbshipit-source-id: ad8d6fb0493e701f60a165a3bca1787d255be008

HISTORY.md

@@ -6,6 +6,7 @@
 * `NO_ITERATORS` is divided into two counters `NO_ITERATOR_CREATED` and `NO_ITERATOR_DELETE`. Both of them are only increasing now, just as other counters.
 ### Bug Fixes
 * Fixed Get correctness bug in the presence of range tombstones where merge operands covered by a range tombstone always result in NotFound.
+* Start populating `NO_FILE_CLOSES` ticker statistic, which was always zero previously.
 
 ## 5.18.0 (11/12/2018)
 ### New Features

db/db_iterator_test.cc

@@ -1951,6 +1951,7 @@ TEST_P(DBIteratorTest, ReadAhead) {
   size_t bytes_read = env_->random_read_bytes_counter_;
   delete iter;
 
+  int64_t num_file_closes = TestGetTickerCount(options, NO_FILE_CLOSES);
   env_->random_read_bytes_counter_ = 0;
   options.statistics->setTickerCount(NO_FILE_OPENS, 0);
   read_options.readahead_size = 1024 * 10;
@@ -1959,7 +1960,10 @@ TEST_P(DBIteratorTest, ReadAhead) {
   int64_t num_file_opens_readahead = TestGetTickerCount(options, NO_FILE_OPENS);
   size_t bytes_read_readahead = env_->random_read_bytes_counter_;
   delete iter;
+  int64_t num_file_closes_readahead =
+      TestGetTickerCount(options, NO_FILE_CLOSES);
   ASSERT_EQ(num_file_opens + 3, num_file_opens_readahead);
+  ASSERT_EQ(num_file_closes + 3, num_file_closes_readahead);
   ASSERT_GT(bytes_read_readahead, bytes_read);
   ASSERT_GT(bytes_read_readahead, read_options.readahead_size * 3);
 

db/table_cache.cc

@@ -42,8 +42,10 @@ static void UnrefEntry(void* arg1, void* arg2) {
   cache->Release(h);
 }
 
-static void DeleteTableReader(void* arg1, void* /*arg2*/) {
+static void DeleteTableReader(void* arg1, void* arg2) {
   TableReader* table_reader = reinterpret_cast<TableReader*>(arg1);
+  Statistics* stats = reinterpret_cast<Statistics*>(arg2);
+  RecordTick(stats, NO_FILE_CLOSES);
   delete table_reader;
 }
 
@@ -249,7 +251,8 @@ InternalIterator* TableCache::NewIterator(
     }
     if (create_new_table_reader) {
       assert(handle == nullptr);
-      result->RegisterCleanup(&DeleteTableReader, table_reader, nullptr);
+      result->RegisterCleanup(&DeleteTableReader, table_reader,
+                              ioptions_.statistics);
     } else if (handle != nullptr) {
       result->RegisterCleanup(&UnrefEntry, cache_, handle);
       handle = nullptr;  // prevent from releasing below