The less flippant explanation is that SQLite can only handle a single writer at any time and when you try to access it with two concurrent writers (or a concurrent reader and writer in some modes) it will by default return a "BUSY" error instead of blocking.

So, if you're were getting unexpected "BUSY" erorrs than, yes, you would be using it incorrectly. However, AIUI, you are always expected to see some amount of BUSY errors during normal, concurrent operation and have to deal with them explicitly. So the fact that you're seeing BUSY errors alone doesn't mean you're doing anything wrong...

To use SQLite correctly from multiple processes, you have to do one of two things:

  - Add explicit code to retry on BUSY errors everywhere you do SQL queries
  - Serialize all access the database, e.g. by using a mutex

GP appears to have chosen the second option.