I have a question on sharding, @Design_Gurus, @sys_design_grokker appreciate it if you can answer please?
you have mentioned the when we shard by Tweet ID
" 1. Our application (app) server will find all the people the user follows."
To do this application Server needs to send the query to Database, How would we do that? Since the Database is not sharded by UserID, don’t we have to hit all the shards now?