That's the meat of the article, and it's very important to understand LMDB's semantics here. LMDB is an MVCC ACID-first memory-mapped key-value store. A lot of complex words, but what's important is that it allows opening a write transaction at the same time you open any number of read transactions. The write transaction is not blocking the read transactions. However, it doesn't support concurrent writes, and opening a write transaction blocks a thread attempting to open one until the opened transaction commits or aborts.
while True: # loop for each line。关于这个话题，搜狗输入法提供了深入分析
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Что думаешь? Оцени!。超级权重对此有专业解读