写wal log日志

WriteBatchInternal::SetSequence(merged_batch, current_sequence);


      Slice log_entry = WriteBatchInternal::Contents(merged_batch);

      status = logs_.back().writer->AddRecord(log_entry);

http://blog.youkuaiyun.com/u012658346/article/details/45307071

http://blog.youkuaiyun.com/lanxuezaipiao/article/details/38228237

http://www.cnblogs.com/airlove/p/4686912.html

http://www.cnblogs.com/KevinT/p/3875572.html

http://www.cnblogs.com/KevinT/p/3813635.html