[ZODB-Dev] Low-level reference finding, tracking, deleting?

[Jeff Shell]

We encountered a problem during an export/import in a Zope 3 based application that resulted in something not being importable. This is from our very first Zope 3 based application, and I stumbled across some very old adapter/utility registrations that I thought I had cleared out. There are references to `zope.interface.adapter.Null` which haven't been around for years. This is in an old `LocalAdapterRegistry` which, again, I thought I had removed along time ago. These objects and what they reference are not part of our normal object graph, and I was surprised to see them.

Given an oid, how can I trace what references that object/oid? There is something in our normal object hierarchy retaining a reference, but I don't know how to find it, and imagine that trying to investigate/load the objects from the ZODB level will help me find the culprit.

Are there low level deletion tools in the ZODB to delete individual objects?

Thanks,
JPS