[Guillaume Tamboise]
Let's say that I have a happily running server, that I get quite a lot of "flipping cache files" with a cache-size at 6000 in my Zope instances, and that I want to improve performances. What should I do?
I suspect you're confusing the ZODB cache (an in-memory cache measured in number of objects -- 6000 is sane for that, although on the small side) with the ZEO client cache (a disk-based cache measured in bytes -- 6000 is way too small for that). The latter cache is the one that "flips". There isn't a "one size fits all" answer for either. Change, experiment, measure, repeat, using your data and your object access patterns on your boxes and your network. Bigger is better until it starts to hurt; the point at which it starts to hurt depends on endless details of your access patterns, OS, HW, etc.