Re: [Revisionmanager-devel] apelib

[Philipp v. W. <ph...@we...>]

Jim,

> the TODO file in the pre-sf distribution mentions using apelib for 
> zodb<->fs synchronization. Apelib is new to me, but I spent some time
> reviewing the code and docs, and gave it a spin on a windows 2k
> machine.
> 
> Do you have any details, notes, or examples to clarify the idea? What
> are the weak points in the current synchronization model? How would 
> apelib reinforce those?

Note that a) ape is still experimental software and b) integration into 
RevisionManager is a nice thought but was never a short-term goal.

RevisionManager has to make a bridge between the ZODB and the 
filesystem. Zope objects reside in the ZODB, CVS can only operate on 
filesystem files. Therefore, RevisionManager synchronizes objects to the 
FS before every CVS action and synchronized the FS to objects after 
every CVS action. This can be very expensive with a lot of objects.

The idea behind ape is that ZODB objects reside on the filesystem as 
standard files and special mappers map objects to files and viceversa. 
This works quite well for standard objects already. The RevisionManager 
scenario looks a bit different, though. Most of the time, you already 
have a (often large) folder sitting in the ZODB.

So in this case, something like a bridge using apelib would have to be 
installed. An object-FS mapper with two storages (ZODB, Filesystem). 
Whatever storage provides a newer version of the object, gets the 
precedence. The other storage is synchronized automatically. That way, 
you save the expensive synchronization processes before and after every 
CVS action.

Back when I thought about this, I emailed Shane Hathaway and he told me 
that it might be possible to do. I looked at apelib's code and 
understood about two thirds. As my time was limited and I'm not a ZODB 
wizard, I forgot the whole idea and concentrated on fixing bugs in the 
already quite stable RevisionManager.
Another advantage apelib had at the time was that it supported property 
synchronization. I implemented my own, very simple property serializer 
and adapters for RevMan 1.3. Apelib still has the advantage of being 
able to synchronize any objects, even non-textual ones.

I hope that cleared it up. I have wasted a few thoughts to some kind of 
RevManNG using apelib and subversion. However, I might shoot for Zope3 
and its filesystem-synchronization features here. If anyone is willing 
to sponsor that or something else, I'd be available again :)

Regards,

Philipp