We found that we could improve performance considerably by tweaking the indices which we;'d neglected, but also identified a number of areas in the rendering of weblog views where some content that changes infrequently was being rendered on every pageload in expensive ZPT iterations and multiple SQL fetches.

There are other caching enhancements that can be made, but the obvious easy win wad to cache the content of most of the sidebars. We have done this now, and the performance improvement is pretty dramatic in big busy blogs with long archive histories and lots of categories, etc.

The downside of caching, of course, is invalidation :o) We are automatically triggering a recalculation of the sidebar contents whenever a discussion or blog item, knlink or knexfile is edited in the weblog. This, however, does not cover the case where the sidebar links are changed; at the moment you have to click a new link in the manage sidebar to refresh the sidebar cache. We'll see about other wayd to trigger an invalidation from sidebar-links changes. I have also considered other methods for managin the siebar links - for instance 3rd party blogroll services, or special delicious accounts. The main advantage of the surrent system (whereby a Plone folder contains all the sidebar links) is that you can easily mak a weblog link to special features and content just by creating subfolders or non-link content types within the sidebar links folder. In any case, the current system will do for a while.

We'll be making further performance improvements over the coming week or two. Watch this space!