One of the most annoying parts of the current way we configure MediaWiki in production is the need for constantly deploying changes for simple actions like:

• pooling/depooling databases
• changing the database weights
• changing the functions a DB server performs (watchlist, recentchanges, vslow, and so on

This basically means being able to populate:

• $wgLBFactoryConf['sectionLoads][$shard]` with a k: v hash of db labels and weights
• `$wgLBFactoryConf['groupLoadsBySection'][$shard][$function] with a k:v hash of db labels and weights

I don't think we should keep that data structure in the variables we'll add to confctl; we should instead aim at making it easy to edit and thus more resistant to mistakes. So first order of business will be to design such data structures.