There are many reasons. The first is that Java is in our opinion the language with the biggest and greatest ecosystem of open source libraries on top of which we can build our software. And this is saving many man-years for us.
I contrast, PostgreSQL extensions need C, which doesn't have these advantages and becomes less productive.
But even more importantly: we don't want to tie it, as much as possible, to PostgreSQL. Maybe, tomorrow, ToroDB would run on other RDBMs :)
If run locally, there's barely performance hit. And it also enables you to run it remotely.
I contrast, PostgreSQL extensions need C, which doesn't have these advantages and becomes less productive.
But even more importantly: we don't want to tie it, as much as possible, to PostgreSQL. Maybe, tomorrow, ToroDB would run on other RDBMs :)
If run locally, there's barely performance hit. And it also enables you to run it remotely.