This message is primary for those of you writing or using alternative MemberAdaptor implementations (e.g. SQL).
Yesterday I checked in a working implementation of a member adaptor based on BerkeleyDB. It seems to greatly improve the memory footprint for really huge lists, at the cost of greater administrative overhead (because you have to know how to setup and manage BerkeleyDBs), and potentially slower performance (I haven't benchmarked it; this is just based on my experience with BerkeleyDB in general). I've found a few things during this experience that point to things we ought to improve. I don't have a lot of time right now, but I wanted to put this out there to start the discussion. I'll quickly mention a few things. - I wanted to hook into the BDB transaction (txn) machinery, and I found a convenient hook. I overloaded MailList.Lock() to include a txn begin, MailList.Save() to do a txn commit, and MailList.Unlock() to do a txn abort. This seems to work well as long as aborting after committing is harmless (it is in BDB). I'd like to get feedback from the SQL folks (or other MemberAdaptor developers) on whether we need more explicit transaction support or whether the basically necessary hooks are already there. - To make this work, however, I found I had to change the order of when the extend.py hook gets run. Specifically, I needed it to run /before/ the list is locked in MailList.__init__(), otherwise locking contructors don't hook into the machinery. I want to commit this change but I don't want to break other MemberAdaptors or extend.py hooks. - We really need to optimize the MemberAdaptor API and the implementations that use them. Especially methods that return lists, e.g. getMembers() and friends. Right now, everything has to return a list, but I could do much better by returning iterators, because I can load my iterator up with a BDB cursor. This has the advantage of not requiring the entire member database to be loaded into memory just to iterate over it. Unfortunately, too much of the rest of the code assumes these methods return lists, and while I started to go down the iterator path, I backed out of it because of the complexity. There are other optimizations that would require a bit more thought. E.g. the admin's Membership List page seems to require that the entire member database be iterated over to chunkify and bucketize. Fixing this probably requires both changes to the u/i and changes to the interface. It also makes life more difficult for OldStyleMemberships, although BDBMemberAdaptor can probably be fairly easily elaborated. I'd like to hear from other member adaptor implementations on their thoughts here. - I'd love for any BerkeleyDB experts to review the BDBMemberAdaptor code, especially in some of the choices I've made for creating and opening the environment. I had a lot of practical problems with this part of the code, especially in getting multiple processes to cooperate reasonably. Any BerkeleyDB experts out there? (I'm fairly happy with the schemas, at least for the current MemberAdaptor API). - I'm leaning heavily toward having this stuff in Mailman 2.2 and /not/ porting it to 2.1.x. Too many changes for a micro release, although it makes project management more complicated, especially in merging fixes back into the 2.1.x maintenance branch. Sigh. Okay, I'm out of time for today. Any feedback will be appreciated, even if I can't respond immediately. Also, the BerkeleyDB based member adaptor seems to work, but should be considered experimental. See the BDBMemberAdaptor.py comments for how to hook this up to a mailing list. There is currently no migration tool from classic member adaptors to BDBMemberAdaptors, although I intend to write such a beast and run a few of my personal lists on the code to flesh things out. Enjoy, -Barry _______________________________________________ Mailman-Developers mailing list [EMAIL PROTECTED] http://mail.python.org/mailman/listinfo/mailman-developers
