sqlite3.OperationalError: database is locked

[themusicgod1]

woke up this morning after having mnemosyne run over night to see:

An unexpected error has occurred.
Please forward the following info to the developers:

Traceback (innermost last):
  File "/usr/lib/python3/dist-packages/mnemosyne/pyqt_ui/main_wdgt.py", line 57, in controller_heartbeat
    self.controller().heartbeat()
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/controllers/default_controller.py", line 56, in heartbeat
    self.database().backup()
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/databases/SQLite.py", line 420, in backup
    self.save()
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/databases/SQLite.py", line 400, in save
    (self.version, "version"))
  File "/usr/lib/python3/dist-packages/mnemosyne/libmnemosyne/databases/_sqlite3.py", line 72, in execute
    self._cursor = self.connection.execute(sql, *args)
 sqlite3.OperationalError: database is locked

if I close this window...it just reopens again.

mnemosyne:
  Installed: 2.4-0.1
  Candidate: 2.4-0.1
ubuntu: bionic 18.04

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: mnemosyne 2.4-0.1
ProcVersionSignature: Ubuntu 4.15.0-23.25-generic 4.15.18
Uname: Linux 4.15.0-23-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Sun Jul 8 09:05:35 2018
InstallationDate: Installed on 2017-04-18 (445 days ago)
InstallationMedia: Ubuntu 17.04 "Zesty Zapus" - Release amd64 (20170412)
PackageArchitecture: all
SourcePackage: mnemosyne
UpgradeStatus: Upgraded to bionic on 2018-04-30 (69 days ago)

[themusicgod1 (themusicgod1)]

killed mnemosyne's 2 windows (both the error and the main window) with xkill and restarted it, seems to be fine since.

[themusicgod1 (themusicgod1)]

Why is this invalid?

[Peter Bienstman (peter-bienstman)]

You no longer have the issue, right? Also, the database could have been locked by any other process.