[Zope] SQL-based LoginManager and subtransactions

[Oliver Bleutgen]

> I haven't been following this discussion, but it sounds like there's
> the potential for SQL operations performed by LoginManager to
> interfere with other SQL operations such as logging uploaded files, in
> the case where the database system does not support nested (sub-)
> transactions.  Correct? 

No, but I'm really not familiar enough with the ZODB machinery and 
zope internals to tell do much more than wild guesses.
The problem seems to be that the ZODB and things like Zcatalog know
about subtransactions (you can disable them with the latter one),
but some (the most) zope db-adapters don't.
Now zope seems to use subtransactions internally and to expect the DAs 
to provide them also (commit_sub), but for now it seems to not completly
clear when and why - see the thread "subtransactions".
For file-uploads the threshold may be <~ 120kb, that is which 
bites people with loginmanager/postgres.
The workaround from I cited should at least solve the zope-error,
but I have no idea if it can hurt.
The best thing would be to properly implement the missing methods in the
DAs, I guess, unfortunately this is above my head for now.

PS: the sybase DA seems to know about commit_sub


cheers,
oliver