Closing a sqlite connection does not clear the -wal and -shm file about diesel

[weiznich]

Thanks for opening this bug report. Can you clarify why you believe this is a bug in diesel, especially as the sqlite documentation says "usually", which implies that there are valid cases where this is not the case and given that diesel explicitly calls sqlite3_close for each opened database object:

diesel/diesel/src/sqlite/connection/raw.rs

Line 248 in 6ef23bd

let close_result = unsafe { ffi::sqlite3_close(self.internal_connection.as_ptr()) };

[hillin]

Hi @weiznich , I don't have all the clue that it's a diesel bug, it's just an abnormality that I observed using diesel.

Per the sqlite documentation, the wal files are not deleted if:

• the last process to have the database open exits without cleanly shutting down the database connection - which should not be the case, as my program is the only process that opens the database, and I guess calling sqlite3_close is sufficient to "cleanly shut down the database connection"?
• or if the SQLITE_FCNTL_PERSIST_WAL file control is used - this one I'm not sure, could there be a place that implicitly sets this flag?

The documentation did not list a third reason, but since the docs are as comprehensive as they can be, I believe it has covered most of the cases. Also for me it's tolerable if the wal files are not deleted occassionally, but apparently in our use cases they are never deleted, which I think should be addressed as a bug.

[weiznich]

This seems to be related to the fact that you use a read only connection.

https://stackoverflow.com/questions/33177784/sqlite3-wal-shm-files-not-deleted#33184948

[hillin]

@weiznich Thanks! That indeed seems to be the problem. A weird behavior in the sqlite implementation but now kind of make sense to me: the -wal file is required to open a db in WAL mode. If sqlite failed to generate the file, it can't even open the db.

(per sqlite docs:)

If the WAL and WAL-index files are missing, then a process that lacks permission to create and initialize those files will not be able to open the database.