In what way does denormalization improve database performance?

Question

I heard a lot about denormalization which was made to improve performance of certain application. But I've never tried to do anything related.

So, I'm just curious, which places in normalized DB makes performance worse or in other words, what are denormalization principles?

How can I use this technique if I need to improve performance?

Answer 1

Denormalization is a time-space trade-off. Normalized data takes less space, but may require join to construct the desired result set, hence more time. If it's denormalized, data are replicated in several places. It then takes more space, but the desired view of the data is readily available.

There are other time-space optimizations, such as

• denormalized view
• precomputed columns

As with any of such approach, this improves reading data (because they are readily available), but updating data becomes more costly (because you need to update the replicated or precomputed data).