[ZODB-Dev] undo and zodb

[Jim Fulton]

Toby Dickenson wrote:
> On Tuesday 03 Sep 2002 2:04 pm, Barry A. Warsaw wrote:
> 

...

>> It has an autopack()
>>method, but I'm still teasing out the semantics of that.  The idea
>>would be to have a storage-wide setting controlling how far back
>>transactions would be kept, although you wouldn't be able to access
>>those older transactions through the api.
>>
> 
> I see Autopack uses a reference count. That is efficient, but it does mean 
> that one small bug or database corruption can lead to it deleting whole 
> sections of your database. Ive no reason to think that it currently has such 
> a bug, but I am hoping to aim for a more fault-tolerant solution for 
> DirectoryStorage.

I don't see that reference counting has much to do with this. If you have
an application that makes objects unreachable, then the unreachable objects
will be removed at a pack.

An application bug like:

   ob = container[oldid]
   del container[oldid]
   get_transaction().commit()
   container[newid] = ob
   get_transaction().commit()

Can cause lossage with FileStorage if it is sufficiently unlucky. ;)
It will definately cause lossage with Packless (although, as I
mentioned in another note, we could fix this). The probability of
lossage with autopack is much lower, but increases with increating
pack frequency.

Jim


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