The discussion revolves around the behavior of the topic_excerpt_maxlength setting. nolo pointed out that changing this setting doesn’t update existing topic excerpts automatically, which can be confusing for community managers. pfaffman noted that rebaking a large number of posts after a setting change might also be confusing, but acknowledged that a note in the setting description could clarify this behavior. JammyDodger suggested adding a description to the setting, such as “If you change this, you must rebake all posts with: ‘rake posts:rebake’”, to make it clearer that a rebake is required.
topic_excerpt_maxlength to a different value.I guess it would also work re-baking all excerpts on the server. But the setting not having an immediate effect is confusing for community managers.
I think that’s a good guess.
Having a setting change start a rebake of a million posts might also be confusing. And it’s not that confusing since you already knew the answer. 
No, a client brought it up. It was confusing to them that changing the setting did not change the excerpt lengths. It was even more confusing when I brought up posts being baked and rebaked… 
Maybe I’m wrong.
I think other settings that require a rebake include such a note in the description. Some other changes rebake posts a few at a time.
I’ve slipped this over to Contribute > UX as I think it’s working as intended. I think a change to the setting description could make this clearer though. It’s currently:
topic excerpt maxlength - Maximum length of a topic excerpt/summary, generated from the first post in a topic.
We do have this on a couple of similar ones - ‘If you change this, you must rebake all posts with: “rake posts:rebake”’, though I don’t know if we could improve on that while we’re at it?