Anki error: sqlite3.DatabaseError: database disk image is malformed

by Daniel Hnyk

I was getting the following error when trying to open Anki after few weeks of inactivity:

An error occurred. It may have been caused by a harmless bug, 
or your deck may have a problem. 
To confirm it's not a problem with your deck, please run Tools > Check Database. 
If that doesn't fix the problem, please copy the following
into a bug report.

and this was the traceback:

Traceback (most recent call last):  
  File "/usr/share/anki/aqt/progress.py", line 69, in handler
    func()
  File "/usr/share/anki/aqt/main.py", line 110, in setupProfile
    self.loadProfile()
  File "/usr/share/anki/aqt/main.py", line 234, in loadProfile
    self.onSync(auto=True)
  File "/usr/share/anki/aqt/main.py", line 598, in onSync
    self.loadCollection()
  File "/usr/share/anki/anki/hooks.py", line 55, in repl
    old(*args, **kwargs)
  File "/usr/share/anki/anki/hooks.py", line 55, in repl
    old(*args, **kwargs)
  File "/usr/share/anki/aqt/main.py", line 290, in loadCollection
    self.moveToState("deckBrowser")
  File "/usr/share/anki/aqt/main.py", line 388, in moveToState
    getattr(self, "_"+state+"State")(oldState, *args)
  File "/usr/share/anki/aqt/main.py", line 392, in _deckBrowserState
    self.deckBrowser.show()
  File "/usr/share/anki/anki/hooks.py", line 55, in repl
    old(*args, **kwargs)
  File "/usr/share/anki/aqt/deckbrowser.py", line 27, in show
    self._renderPage()
  File "/usr/share/anki/aqt/deckbrowser.py", line 142, in _renderPage
    self._dueTree = self.mw.col.sched.deckDueTree()
  File "/usr/share/anki/anki/sched.py", line 261, in deckDueTree
    return self._groupChildren(self.deckDueList())
  File "/usr/share/anki/anki/sched.py", line 219, in deckDueList
    self.col.decks.recoverOrphans()
  File "/usr/share/anki/anki/decks.py", line 417, in recoverOrphans
    ids2str(dids))
  File "/usr/share/anki/anki/db.py", line 39, in execute
    res = self._db.execute(sql, a)
sqlite3.DatabaseError: database disk image is malformed

I unfortunately hadn't found any other solution then to move the default Anki folder (usually ~/Documents/Anki on windows and ~/Anki in Linux) to some other place, run Anki again and then let Anki synchronize data from server. If you haven't synchronized data for a while, you could retrieve them from the old backup folder (old_anki/your_profile_name/backups/).