Fix small issues (#5896)

Summary:
The individual commits in this PR should be self-explanatory.
All small and _very_ low-priority changes.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/5896

Reviewed By: riversand963

Differential Revision: D18065108

Pulled By: mrambacher

fbshipit-source-id: 236b1a1d9d21f982cc08aa67027108dde5eaf280

include/rocksdb/status.h

@@ -451,12 +451,11 @@ class Status {
   std::string ToString() const;
 
  protected:
-  // A nullptr state_ (which is always the case for OK) means the message
-  // is empty, else state_ points to message.
-
   Code code_;
   SubCode subcode_;
   Severity sev_;
+  // A nullptr state_ (which is at least the case for OK) means the extra
+  // message is empty.
   const char* state_;
 #ifdef ROCKSDB_ASSERT_STATUS_CHECKED
   mutable bool checked_ = false;

utilities/transactions/transaction_base.h

@@ -202,7 +202,8 @@ class TransactionBaseImpl : public Transaction {
   }
 
   const Snapshot* GetSnapshot() const override {
-    return snapshot_ ? snapshot_.get() : nullptr;
+    // will return nullptr when there is no snapshot
+    return snapshot_.get();
   }
 
   virtual void SetSnapshot() override;

utilities/write_batch_with_index/write_batch_with_index_internal.h

@@ -122,7 +122,7 @@ struct WriteBatchIndexEntry {
   // make the entry just larger than all entries with the search key so
   // SeekForPrev() will see all the keys with the same key.
   size_t offset;
-  uint32_t column_family;  // c1olumn family of the entry.
+  uint32_t column_family;  // column family of the entry.
   size_t key_offset;       // offset of the key in write batch's string buffer.
   size_t key_size;         // size of the key. kFlagMinInCf indicates
                            // that this is a dummy look up entry for