undefined | Better HN

0 pointsthreeseed10y ago0 comments

How exactly do you think eBay, GMail, Facebook etc work ? They aren't relying on relational database joins.

If you want to write a truly scalable application you structure everything such that you do joins in your application layer.

http://highscalability.com/ebay-architecture

And in the case of MongoDB you avoid joins since it is a document database. You embed data instead.

0 comments

4 comments · 1 top-level

ngrilly10y ago· 3 in thread

Not everybody works at eBay, GMail or Facebook scale.

Most applications fit very well in a single server. For example, Stack Overflow runs on a single instance of SQL Server, replicated to a slave in another data center. In such a case, the convenience of joins and transactions is priceless.

And even at scale, it makes sense to rely on joins and transactions. The perfect example is AdWords that runs of F1 and Spanner:

"Our users needed complex queries and joins, which meant they had to carefully shard their data, and resharding data without breaking applications was challenging."

http://static.googleusercontent.com/media/research.google.co...

threeseedOP10y ago

Exactly. But many of us do have apps that are beyond the capabilities of a single instance.

And in this situation the rule of thumb is to do joins in your application layer so you can store different types data (e.g. graph/document/relational/unstructured) in different systems and easily cache where needed.

The fact that so many new databases have been created in the last decade suggests that there are a lot of people who do fall into this camp.

theseoafs10y ago

A lot of us have apps that are beyond the performance requirements of Stack Overflow?

1 more reply

wcummings10y ago

There are also organizational requirements that push people away from joins (different teams responsible for warehousing different data in a large organization) and high performance applications which pre-summarize data (adtech).

j / k navigate · click thread line to collapse