On: Ask HN: Do you use foreign keys in relational data...

[goto11]

Depends. Denormalized means the database contains redundant data. If a query have to scan 10x or 100x as many rows due to redundant data, it is obviously going to be slower. But it is hard to say anything general since denormalization will make some queries faster and other queries slower.

[skyde → goto11]

with good index you will not scan more rows.

But each query will use a different copy of the same data instead of joining with the same copy.

Storing both copy in memory take more space so you can’t cache as much in memory.

I’m not talking redis or memcached but the page cache inside the sql engine.