Not sure if we can detect "locked by anti-virus", but SQLite is known to give "blocked" failures when database is locked for write. We could inspect result and attempt to reconnect 3 times after 50, 100, and 200ms for example.

Johannes, what do you think?

After reading into the code a bit, I couldn't agree more.
Currently, we handle errors during SQLite connection establishment non-specifically. There is a retry mechanism that does the following N -times:

1. close the connection if open
2. create a backup
3. delete the current database file
4. retry

where n is 2. This means that the database is reset every time a database error occurs during the establishment of the connection. This can hardly be the expected behavior, especially in cases where the error is potentially temporary. (Also, it doesn't seem to make much sense to try to create a backup when memory is full, but that's just as an aside).

Instead, depending on the error, we can do three things:

1. retry N times immediately with reset (current situation). For cases where it is a database file problem.
2. retry with exponential backoff, without resetting the database. For external problems, which may be fixed after some time
3. give up directly if there is no hope

To get closer to this, let's first have a look at the possible errors. At https://searchfox.org/mozilla-central/source/toolkit/modules/Sqlite.sys.mjs#134-172 you can find a list of all errors and their assignment to mozIStorageError. These errors can be grouped into three different categories depending on their treatment:

Database File Errors

Errors on the file can only be fixed by resetting the database:

• file corrupted
• too large
• unexpected

Suspected Temporary Errors

In the case of an error that will probably be fixed in the short term, a retry is worthwhile:

• abort
• locked
• busy
• restriction
• memory io error

Potentially Permanent System Errors

If these are fundamental errors, which are likely to be of longer duration, there is nothing to do. (For simplicity, however, these errors can be handled by retry).

• access denied
• write protected
• no memory

What do you think?

Confirmed that in case of an ACCESS_DENIED error, the database is reset.

https://hg.mozilla.org/mozilla-central/rev/bc65f490e5cf