There were half a million restaurants back then or thereabout, and they wanted to store ratings and comments.
That is not something you'd be able to put on one single database in 2004.
Why didn't they simplify afterward I can't imagine, but I can see how a business directory at that age looked at the numbers and went yeah not in a database.
Back in 2004 I was running larger MySQL databases than yelp has now:
https://www.enterpriseappstoday.com/stats/yelp-statistics.ht...
> That is not something you'd be able to put on one single database in 2004.
Sorry, but it was, plenty of companies had much larger databases back then running plain old master slave replication.
But even if it wasn't: just don't run it all on one db? Nothing says you need to be able to join on the restaurant table and the comments table. Put them on different servers. That's all you're doing with Casandra anyway.
Also, whether you need a highly available database for a company like yelp is an implementation detail.
Oh no, the database is down, how will Jonny decide where to go for lunch now?!
> Also, whether you need a highly available database for a company like yelp is an implementation detail.
You surely know better than them what they need, that's impressive.
I used to work at Yelp, and at least at that time, a big use case of Cassandra was basically for what were essentially materialized views created from log data. At that point in time, MySQL or logs were the "sources of truth", but there were enough transactions going on that it made sense to have things like Cassandra around too for some of the other use cases.