I uploaded new changesets to http://code.google.com/p/pharo/issues/detail?id=3002 I tested applying them in Pharo-Core-#12159 and then updating an image after that. After update: MCMethodDefinition cachedDefinitions size is 18668 But image don't feels slow. As a side note, i recommend to review the MC caching mechanism towards avoiding putting so much load on finalization process (such as scanning 18k entries to find dead objects). This is actually the purpose of new finalization scheme: - it allows to avoid scanning whole weak dictionary in order to get rid of expired associations. I'm already implemented a variant of self-cleaning weak dictionary for Magma, which using new finalization scheme, and avoids scanning huge number of entries to discover few of them, which became garbage. -- Best regards, Igor Stasenko AKA sig.