I wish there was an SQL option to cause a fatal error if it needs to do a table scan. This would be very useful on test systems, at least.
NoSQL forces discipline which is a good thing, preventing "late" performance optimization when in production.
NoSQL forces discipline which is a good thing, preventing "late" performance optimization when in production.
If you have a table with four rows in it, would you like the database to give you errors when you do a full scan on it?
What you want is an option to throw errors when a query takes too long to execute and most products already have this in the form of a statement timeout parameter.
On a separate note, the balance between "late" optimization and "premature" optimization is thin indeed... These test systems need to run with the same data and on the same hardware as your main database to give meaningful results, so it's generally unavoidable to do some kind of performance tweaking on the already deployed code. And of course as the data distribution and its amount changes, you need to keep on optimizing...
In MongoDB (and maybe others too) there exists an option to fail when doing a table scan so that you know immediately while developing that there exists a potential for things to go awry at some later point. You can fix that now by either re-thinking your data structure, re-thinking your query, or adding appropriate indexes.
MySQL's slow query log is good for reactive development instead of proactive development.
I think its an indispensable feature.
I still don't see what a setting that gives errors when a particular access method has been chosen would be good for.
You don't care about the plan, you care about how fast the query runs.
You'll always have to do reactive development when trying to get good performance. There is only so much simulating and testing you can do and real data volume and distribution changes all the time.
Many developers have been burned by trying to optimize their queries and indexes too early. The query planner, although sometimes unpredictable, is generally better than developers at predicting the performance of a particular execution plan. Table scans are also preferable in certain situations.
Relying on the fact that RDBMS have sophisticated query planner (as opposed to MongoDB) is not a sign of "reactive development". It just means that you should test your queries (and your indexes) with close-to-production data, and, as the data grows and evolves, continue to test, because the best execution plan might change.
At least for interactive apps, NoSQL wins.