questions about LMDB

["Shu, Xinxin" <xinxin.shu@intel.com>]

Hi list ,

Recently I read docs about lmdb , there are two sentences 
1) readers do not block writers 
2) writers do not block readers
I can understand 'readers do not block writers' , but cannot understand the second one , can someone help explain , how lmdb achieve 'writers do not block readers',  below is my understandings , please correct me if anything wrong.
 if the access pattern is write - read, since lmdb only support two version of data ,  when the write has been started but not committed ,  the concurrent read may read stale data since write has not been committed.

Cheers,
xinxin