SQLite can promote connections, but it does not demote them back to read-only. As I understand, when a database connection is tainted by a single write, it's lock on SQLite file in promoted to write lock, which prevents other processes from opening any kind of connection to it.

Our Django setup needs multiple processes to work around the Grand Interpreter Lock. Disabling connection reuse in Django config slightly changed the behavior we observed, but didn't solve the performance problem.