This was an intentional choice we made for a couple of reasons. The most pragmatic one was that we don't have an optimizer and we thought that secondary indexes could still be useful to a lot of people without one. And we've found it's always better to ship early and get feedback sooner rather than later.
Another reason though is we're not totally sure we're sold on the state of the art of query optimizers. From what we've seen they can introduce a number of non intuitive behaviors and it can be hard to tell which operations will use which index. Query optimizers are nice when they work correctly but they don't always work correctly so for the first release of secondary indexes we opted to make something that had very clear precise semantics and then build on it. We will eventually have a query optimizer but it's a big problem and we don't just want to implement what others have because we think we can do better.
This was an intentional choice we made for a couple of reasons. The most pragmatic one was that we don't have an optimizer and we thought that secondary indexes could still be useful to a lot of people without one. And we've found it's always better to ship early and get feedback sooner rather than later.
Another reason though is we're not totally sure we're sold on the state of the art of query optimizers. From what we've seen they can introduce a number of non intuitive behaviors and it can be hard to tell which operations will use which index. Query optimizers are nice when they work correctly but they don't always work correctly so for the first release of secondary indexes we opted to make something that had very clear precise semantics and then build on it. We will eventually have a query optimizer but it's a big problem and we don't just want to implement what others have because we think we can do better.