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file/file_prefetch_buffer.cc

@@ -372,8 +372,11 @@ void FilePrefetchBuffer::ReadAheadSizeTuning(
   assert(updated_start_offset < updated_end_offset);
 
   if (!read_curr_block) {
+    // Handle the case when callback added block handles which are already
+    // prefetched and nothing new needs to be prefetched. In that case end
+    // offset updated by callback will be less than prev_buf_end_offset which
+    // means data has been already prefetched.
     if (updated_end_offset <= prev_buf_end_offset) {
-      // It can be when this callback only added previous block handles.
       start_offset = end_offset = prev_buf_end_offset;
       return;
     }

table/table_test.cc

@@ -1128,9 +1128,7 @@ class BlockBasedTableTest
       virtual public ::testing::WithParamInterface<uint32_t> {
  public:
   BlockBasedTableTest() : format_(GetParam()) {
-    std::unique_ptr<Env> env(
-        new CompositeEnvWrapper(Env::Default(), FileSystem::Default()));
-    env_ = env.get();
+    env_ = Env::Default();
   }
 
   BlockBasedTableOptions GetBlockBasedTableOptions() {