[Zope-dev] Cache growing during single REQUEST

[Chris Withers]

Tim Peters wrote:
> "Multiversion concurrency control" (MVCC for short) is the next step.  If no
> other crises intervene, Jeremy and I will start implementing that on the
> ZODB3 3.2 branch (most likely that branch -- can't swear to it) soon
> (ditto).

 From Jeremy's recent notes, I think it'll be the Zope 2.6 branch...

> You can google on the phrase to get a ton of more-or-less abstract overviews
> of the concept.  The short course in ZODB is that, when MVCC is in effect, a
> read will return the state of the object as of the time the current
> transaction began, even if the object has subsequently been modified by some
> other transaction.

Sounds great :-) If you need any implementations testing, do let me know!

> The overriding concern in all schemes is that you don't see inconsistent
> data.

Yep.

> The current ReadConflictError prevents you from seeing inconsistent
> data by preventing you from loading objects that have changed since your
> current transaction began.  

Indeed, butthat could eb a lot of things, and often in situations where ti 
wouldn't matter, as long as the data is consistent...

> MVCC prevents it by (possibly) delivering
> non-current object states.  I don't think either can be viewed as a pure
> win.  The ways in which ReadConflictError loses are obvious to people here
> because they've experienced them.  The ways in which MVCC loses will become
> obvious later <0.9 wink>.

Any ideas what they'll be yet?

Chris