Obviously a single query is faster than a join, but it&#x27;s very hard to guarantee that you&#x27;ll always be making that single query.<p>Data inconsistency is not about concurrency. See this example on Wikipedia illustrating why 3NF is necessary: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Third_normal_form#.22Nothing_but_the_key.22" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Third_normal_form#.22Nothing_b...</a><p>In that example, &quot;Al Fredrickson&quot; can potentially have 2 birthdays even in an entirely single threaded app.<p>I&#x27;m really curious to hear a use case where Mongo was actually significantly faster than Postgres. Could you give a toy example that illustrates the flavor of the problem?