Table name: growthexperiments_user_impact
Cluster: I'm assuming it should go to x1 like all other GrowthExperiments tables.

Use case: cache secondary data related to a user's activity that is expensive to calculate (such as edited articles, thanks received, number of pageviews to the edited articles). See mw:Growth/Positive reinforcement for more information.

Table schema: json, sql

Expected usage patterns: basically a key-value store keyed by user ID, with some additional expiration mechanics. Web requests will get/set a single value corresponding to the current user when someone visits Special:Homepage (about 10K times a day); a maintenance script will batch-update values. (See store patch; maintenance script still WIP.)

Expected storage needs: about 5K per record (a JSON blob which we currently make no effort to compact), stored for 1) users who have registered in the last two weeks, 2) users who have registered within a year and made at least one edit, 3) users who have visited Special:Homepage recently. Using the guesstimate that enwiki is about half of all Wikimedia user accounts, that's about 150K acounts for 1), 1M accounts for 2), and 3) is going to be insignificant in comparison, so expected storage space is something like 6G. (The data is only actually needed when the user visits Special:Homepage, so we can almost arbitrarily reduce this if needed, at some UX cost for people who do visit their homepage but infrequently.)