MySQL vs Redis for storing follower/following users

Question

I'm trying to find the best candidate for storing the follower/following user data, I was thinking initially to store it in Redis in a set where user -> set of user ids but then I thought about scenario where there is over 1 million or even 10 million followers for a user, how Redis would handle such a huge set? also there is no way I can do pagination on a set in redis, I have to retrieve the whole set which will not work if a user wants to browse who following after him. If I store it in MySQL I can definitely do pagination but it might take a long time fetching 10 million records from the database whenever I have to build the user feed, I can do this in old batch fashion but it still sounds pretty painful whenever a user who has many followers will post something and then processing these 10 million records would take forever just for fetching his followers. Would it be worthwhile to store it in MySQL for pagination (mainly Frontend) and in Redis for the event-driven messaging which builds the activity feed?

Answer 1

It's a personal decision whether to use redis or mysql for this task. Both will have no problem with those 10 million records.

MySQL has the LIMIT x,y command for getting a subset of the followers from the database.

For redis you can use sorted sets and use the userid of the follower or the time user started following as score for an sorted set. And like MySQL redis supports getting a subset of the large sorted set.