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

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


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?


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