I'm not too sure if you are arguing for or against the commercial RDBMS.
To me, that sounds like a pretty good argument against it - the great thing about MySQL/Postgres+Sharding is that it scales down, as well as up. You can start out with a single server, then gradually add in extra servers as you need them. With the "single big DB server model" it doesn't work like that - you have to make a pretty decent investment early on in the software licence, build your software to use it, and then the pricing isn't linear, either.
Plus, the backup/redundancy thing sucks too - with sharded MySQL you need a couple of spare cheap servers, but with Oracle etc you need to pay twice for the licence and a second server.
OTOH, in a corporate environment it's much easier to predict your usage and the pricing is easier to justify. Also your priority is safety+justifiability first rather than price or even price/performance.
Comments
I'm not too sure if you are arguing for or against the commercial RDBMS.
To me, that sounds like a pretty good argument against it - the great thing about MySQL/Postgres+Sharding is that it scales down, as well as up. You can start out with a single server, then gradually add in extra servers as you need them. With the "single big DB server model" it doesn't work like that - you have to make a pretty decent investment early on in the software licence, build your software to use it, and then the pricing isn't linear, either.
Plus, the backup/redundancy thing sucks too - with sharded MySQL you need a couple of spare cheap servers, but with Oracle etc you need to pay twice for the licence and a second server.
OTOH, in a corporate environment it's much easier to predict your usage and the pricing is easier to justify. Also your priority is safety+justifiability first rather than price or even price/performance.