Fix memleak when DB::DeleteFile()

Summary:
Because the corresponding read_first_record_cache_ item wasn't
erased, memory leaked.
Closes https://github.com/facebook/rocksdb/pull/1712

Differential Revision: D4363654

Pulled By: ajkr

fbshipit-source-id: 7da1adcfc8c380e4ffe05b8769fc2221ad17a225

db/db_impl.cc

@@ -2047,8 +2047,7 @@ Status DBImpl::DeleteFile(std::string name) {
                       name.c_str());
       return Status::NotSupported("Delete only supported for archived logs");
     }
-    status =
+    status = wal_manager_.DeleteFile(name, number);
-        env_->DeleteFile(immutable_db_options_.wal_dir + "/" + name.c_str());
     if (!status.ok()) {
       ROCKS_LOG_ERROR(immutable_db_options_.info_log,
                       "DeleteFile %s failed -- %s.\n", name.c_str(),

db/wal_manager.cc

@@ -39,6 +39,15 @@ namespace rocksdb {
 
 #ifndef ROCKSDB_LITE
 
+Status WalManager::DeleteFile(const std::string& fname, uint64_t number) {
+  auto s = env_->DeleteFile(db_options_.wal_dir + "/" + fname);
+  if (s.ok()) {
+    MutexLock l(&read_first_record_cache_mutex_);
+    read_first_record_cache_.erase(number);
+  }
+  return s;
+}
+
 Status WalManager::GetSortedWalFiles(VectorLogPtr& files) {
   // First get sorted files in db dir, then get sorted files from archived
   // dir, to avoid a race condition where a log file is moved to archived

db/wal_manager.h

@@ -49,6 +49,8 @@ class WalManager {
 
   void ArchiveWALFile(const std::string& fname, uint64_t number);
 
+  Status DeleteFile(const std::string& fname, uint64_t number);
+
   Status TEST_ReadFirstRecord(const WalFileType type, const uint64_t number,
                               SequenceNumber* sequence) {
     return ReadFirstRecord(type, number, sequence);