[ZODB-Dev] Savepoints are invalidated once they are used

[Jeremy Hylton]

IIRC, the old implementation of savepoints kept a copy of the index at
the time the savepoint was taken so that you could rollback to it
multiple times.  I don't think there's any way to avoid such a copy.

Jeremy

On 7/11/05, Tim Peters <tim at zope.com> wrote:
> [Tim Peters]
> > ...
> > The good news is that, while it was hard to find, it's a one-line repair.
> 
> Alas, that wasn't the end of it either.  I think I'm at the end now, and all
> the tests are passing again (including new tests to provoke new problems I
> found).
> 
> A savepoint (of the data manager Connection flavor) remembers the TmpStore
> index at the time the savepoint was made.  When a savepoint could be used
> only once, the savepoint only needed to make sure it had a copy of the index
> at the time the savepoint was _made_.  But when a savepoint can be reused,
> even the TmpStore.reset() line
> 
>     self.index = index
> 
> was a source of subtle bugs (later mutations to `self.index` showed up in
> `index` too, and `index` there is typically taken from a savepoint's "this
> is what the world looked like when I was new" state -- mutating that was
> harmless before because the rollback could never be used again, but became
> disastrous when allowing re-use).
> 
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