Can/should I use WeakReference in my complex object structure with db4o?

Question

I'm considering to port an application to db4o. The data model consists of lots of small objects with a lot of references between each other. For example, I have a book which points to an author and chapter. Chapters have sections, sections have large blobs of text, images, and they reference characters mentioned.

I think it should be possible to keep the meta structure in memory (everything except the text blobs) but I was wondering whether I could use some clever trick involving WeakReference so db4o would just keep the part of the model in memory that I really need (i.e. which I've been using recently).

The same is true for the text blobs (which should be around 1-10KB). Is it possible to get a String without having to worry about the DB layer and without having to query for the text blob using an artificial ID inside the getter and without using a hard reference which keeps the whole text in memory all the time?

Answer 1

I've not used db40, or any ORM/OODB product recently, however it would strike me that this kind of memory management & graph management feature should be part of the framework itself rather than something you build on top of it. If Versant's db40 doesn't offer this it might be worth you looking into another product instead that does offer it. So, I realise not the answer your looking for, but leveraging the framework would be my first port of call.

Answer 2

Hi!

Turning off WeakReferences is mostly used for performance tuning. The downsides to this approach are not negligible - so be careful. I would not recommend it.

Controlling memory usage should be done using activation features. Activation can help you keep only part of you model in memory and weakreferences will help you GC objects no longer used. I think that's the way to go.

Also - you can post your questions to db4o forums to get help from the db4o community.

Goran