On 05/18/2010 10:08 PM, Jim Fulton wrote: > The design of ZODB views pickles as opaque to storages. Storages > primarily store strings. I have always assumed that writing wrapper > storages for compression or encryption would be easy. I was wrong. :) > > Storages sometimes need to know about pickles: > > A. When doing garbage collection, a storage (or garbage collector) > needs to extract object references. > > B. When doing conflict resolution, the conflict-resolution code needs > to be able to extract state from object records. > > C. When doing blob-aware iteration, a storage needs to be able to > recognize blob records. > > D. When raising conflict errors, the exception instances *want* to get > the object class name from the database record. > > (A) was dealt with by the existing way the referencesf function was > passed into storage pack functions.
Wow, good to know about those! Thanks for the info! > I dealt (B) and (C) by expanding and renaming the interface of objects > passed to the storage registerDB call. These objects now provide an > up-call mechanism from a storage to anything that might wrap it, > including databases, storage servers, and intermediate wrapping > layers. > > I punted on (D). You can't always get what you want. :) > > I'm mostly convinced what I've done is reasonable, although I'm just a > little uncomfortable. It has always been the theory that storages > can't count on the contents of database records. Now that is > reality. > > I've decided I really want to provide a database compression option. I > could have built something directly into ZODB or used a wrapper > storage. I chose the later because it was more flexible. I think I > would have run into the same issues without a wrapper storage. > > Soon I expect to release a wrapper storage implementation that > provides record compression. Cool! :) -- Christian Theune · c...@gocept.com gocept gmbh & co. kg · forsterstraße 29 · 06112 halle (saale) · germany http://gocept.com · tel +49 345 1229889 0 · fax +49 345 1229889 1 Zope and Plone consulting and development _______________________________________________ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org https://mail.zope.org/mailman/listinfo/zodb-dev
