The crashes on ExFAT are caused by a bug in the MacOS ExFAT driver. It is unclear whether other OSes are affected too.
https://github.com/mattn/go-sqlite3/issues/1355
We now utilize sqlite's concurrency features by creating a write pool (size 1) and a read pool, and can eliminate our own RWMutex, which prevents reads at the same time as writes. Sqlite's WAL mode allows reads concurrent with writes, and our code is much cleaner.
Still need to do similar for the thumbnail DB.
Also could look into using prepared statements for more efficiency gains.
