Comment 2 for bug 1045983

Marked this medium because there are probably workaround solutions to avoid having to truncate a non-temporary volume. For example, and application could simply delete all the trees in the volume.

More fundamentally, we need to incorporate management of Tree and Volume instances into the transaction protocol and deal with issues such as transaction A needing to read an old copy of the volume while Transaction B is truncating it. A design for these improvements is underway.