[Devilboy]

I seriously doubt that this is true. SQL databases are extremely easy to adjust. Hell you can add columns on your live database in the middle of the day if you want. Removing data is harder but normally you don't have to delete columns just to launch your new code.

Another thing to remember is that most SQL systems are mature and there is pretty much always very good tools available to do any kind of changes you may need to do.

[benblack]

The existence of great tools for relational databases is a compelling argument for using them. As I said in the article, starting off using a single, monolithic relational store is a successful approach employed by many, successful companies. I would suggest, though, that the rest of your comment indicates a lack of experience with relational databases at large-scale. One metric provided by Twitter in a presentation was that an ALTER TABLE command took 2 weeks to run on a previously centralized relational database. Perhaps someone from Twitter can add some color to that anecdote.

tl;dr - Scale breaks your assumptions.

[Devilboy]

Scale just breaks MySQL.

[benblack]

If the answer is "Spend millions on Oracle", people will be motivated to ask a different question.

[gaius]

Like I say, in business there is no cheap or expensive. There's worth the money, or not.

Yes, Oracle costs money. But so does "rolling your own". How much of their VCs cash has say Twitter spent doing that? Yes, Oracle "locks you in". But your own legacy code locks you in whatever platform you've built it on.

[benblack]

In the specific case of FlockDB, that's actually not the case as the shards are modular. SQLShard is one implementation. There was an experimental Redis shard implementation, as well. You might be both overestimating the cost of building things like this and underestimating the enormous drag of using closed source components in these systems. If you've personally built online services this big with Oracle, well done. What did it cost?

[gaius]

Once you have hash joins, shards start to look awfully restrictive compared to partitions... MySQL (et al, I don't know about FlockDB) can freely shard because they're not losing functionality they don't have in the first place.

Maybe I'm not a good example because I've mainly worked in financial services, but nearly every Oracle project I've worked on has been wildly profitable, and most have been at the level (in terms of transactional throughput, and in terms of features that were cheaper to buy than build) at which there are only really two choices, Oracle or DB2.

[Devilboy]

You don't have to spend millions on Oracle. You can spend thousands on SQL Server or get PostgreSQL for nothing too.

[1337p337]

What scale? How many concurrent users of your specific site break MySQL, and how many concurrent users do you have? Not answering or considering those questions is what leads to premature scaling.