Detecting mismatched WAL files

(1) By fernandocc on 2020-09-25 19:00:00

Hello,

In WAL journaling mode, if a `-wal` file exists at the time the first database connection is opened, SQLite will attempt to integrate those changes. However, I couldn't find any documentation describing what happens if the WAL file is accidentally mismatched. For instance, a user could accidentally restore a backup of the main database file, but fail to remove an existing `-wal` file.

In my very limited testing, it seems to me that SQLite blindly accepts a `-wal` file without any sort of validation. Is this the expected behavior? And if so, is there a way to make SQLite validate and fail to checkpoint if the `-wal` file is somehow mismatched?

Thank you in advance.

(2) By David Raymond (dvdraymond) on 2020-09-28 14:47:08 in reply to 1 [link]

That is section 1.4 in [How To Corrupt An SQLite Database File](https://www.sqlite.org/howtocorrupt.html) and is indeed the expected behavior.

You can see what's in the header for the WAL file [here](https://www.sqlite.org/fileformat2.html#the_write_ahead_log)
"What database did it come from" is stored as the name of the file itself. I'm not quite sure what else you could put in there as a validation. Maybe the file change counter? Or does that not get used in WAL mode?