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Correct me if I'm misunderstanding. Refer to the following sentence:

Stack Overflow copied a key part of the Wikipedia database design. This turned out to be a mistake which will need massive and painful database refactoring to fix. The refactorings will be to avoid excessive joins in a lot of key queries. This is the key lesson from giant multi-terabyte table schemas (like Google’s BigTable) which are completely join-free. This is significant because Stack Overflow's database is almost completely in RAM and the joins still exact too high a cost.1

Actually I'm trying to pass from the interest on single technology like Asp.net MVC to architectures design.

Can you better clarify the quoted sentence?

[1] http://highscalability.com/stack-overflow-architecture

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1 Answer 1

up vote 7 down vote accepted

You've misread the directionality of the quote.

JOINs are generally discouraged for high-volume systems, because they are expensive (because of I/O being necessary more than one table). SO put their database into RAM specifically to avoid being hit by double disk I/O costs, and it turns out that even without physical I/O, the double table searching is still too slow. That shows you just how inefficient JOINs are on large volumes of data.

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But that's impressive... How can it be? A similar sentence seems to show that relational database are not enough efficient on one of their primary task.. (handling 3NF).. I think it really worths a question here.. –  M.F05051985 Apr 7 at 14:06

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