On Fri, Sep 17, 2010 at 6:15 PM, Jim Fulton <jim@zope.com> wrote:

I suspect that the shenanigans played by the ZODB persistent cache implementation is running afoul of some changes in the garbage collection implementation in Python 2.7.

My suspicion was correct. :)

See https://bugs.launchpad.net/zodb/+bug/641481

Fixed.

The person reporting this was running a Python compiled in debug mode. This will sometimes detect subtle memory management bugs not detected with a normal build.  ZODB's tests pass with a normal Python 2.7 build and with a debug Python 2.6 build.

I've tracked one source of crash in a debug build to the cache's attempts to manage weak references to ghosts. Even hacking around this, there are other crashes that, I assume, are related. :(

I'll dig further, but I strongly suspect that moving to Python 2.7 will require a cache reimplementation that uses real Python weak references.  This won't happen in ZODB 3.10.

Fortunately, the fix didn't require it.

If there is anyone on this list who has knowledge of Python GC internals, I'd love to get some help. :)

Thanks to Tim Peters for helping me figure out the fix. Jim -- Jim Fulton