default shelve on linux corrupts, does different DB system help?

Paul Sijben paul.sijben at xs4all.nl
Sun Mar 22 10:19:34 CET 2009


Thanks very much for a clear and concise explanation of the problem and
the solution!

I am implementing it now in my system. Luckily we caught this one during
testing so no important data has been lost.

Unfortunately windows does not seem to support gdbm. But in our case,
everything that is on the windows client is also available on the linux
server, so we can recreate the DB at the expense of some bandwidth in
case of failures.

Paul

skip at pobox.com wrote:
>     Paul> I have the problem that my shelve(s) sometimes corrupt (looks like
>     Paul> it has after python has run out of threads).
>
>     Paul> I am using the default shelve so on linux I get the dbhash
>     Paul> version.  Is there a different DB type I can choose that is known
>     Paul> to be more resilient? And if so, what is the elegant way of doing
>     Paul> that?
>
> You don't say what version of Python you're using or what version of the
> Berkeley DB library underpins your installation, but I am going to guess it
> is 1.85.  This has been known to have serious bugs for over a decade.  (Just
> in the hash file implementation.  The btree and recnum formats are ok.
> Unfortunately, the hash file implementation is what everybody has always
> gravitated to.  Sort of like moths to a flame...)
>
> If that's the case, simply pick some other dbm file format for your shelves,
> e.g.:
>
>     >>> import gdbm
>     >>> import shelve
>     >>> f = gdbm.open("/tmp/trash.db", "c")
>     >>> f.close()
>     >>> db = shelve.open("/tmp/trash.db")
>     >>> db["mike"] = "sharon" 
>     >>> db["4"] = 5
>     >>> db.keys()
>     ['4', 'mike']
>     >>> db.close()
>     >>> f = gdbm.open("/tmp/trash.db", "c")
>     >>> f.keys()
>     ['4', 'mike']
>     >>> f['4']
>     'I5\n.'
>     >>> f['mike']
>     "S'sharon'\np1\n."
>
> As for "uncorrupting" your existing database, see if your Linux distribution
> has a db_recover program.  If it does, you might be able to retrieve your
> data, though in the case of BerkDB 1.85's hash file I'm skeptical that can
> be done.  I hope you weren't storing something valuable in it like your bank
> account passwords.
>
>   



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