[ZODB-Dev] Re: [Dev] ZODB is not a Storage Technology (Re: other formats )

[Jeremy Hylton]

As you noted, the description of versions isn't quite right.  Versions
provide a mechanism to lock objects over a series of transactions.
The locking mechanism can be important for an application that makes
changes and takes a long time to run.  ZODB uses optimistic
concurrency control, so a long running transaction normally has a
higher chance of seeing a conflict.

Once an object is modified in a version, it is locked.  No other
transaction can modify the object unless it is running in the same
version.  The changes to the object aren't visible until the version
is committed, at which point the object(s) are unlocked.

Jeremy