Notifications: Performance issues at scale?

[#1]

Did some local testing and noticed that if, for example, 3 people are following a blog post and someone leaves a comment, there are 5 Mongo documents created:

• 1x Comment
• 1x Activity, for the user who commented
• 3x Notifications, for each user following this blog post

What happens if we had, again just for example, 15,000 users following a blog post...!

1. Would that generate 15,002 Mongo documents each time a comment was posted?
2. Would this slow down the time it takes to post each comment?
3. Couldn't this quickly get out of hand, if you had a large number of blog posts that users were actively following and commenting on?

Version: AEM 6.2 with Communities FP1 & FP2
SRP Config: Mongo DB SRP (MSRP)

[#2]

Thank you so much for the reply, Dan. Makes a bit more sense after reading a couple articles on it.

For anyone else that may come across this post in the future, this is the article I found, and the links that it contains:

• Write-based fan-out vs read-based fan-out : http://rubanm.tumblr.com/post/59561467766/write-based-fan-out-vs-read-based-fan-out
• The Architecture Twitter Uses to Deal with 150M Active Users : http://highscalability.com/blog/2013/7/8/the-architecture-twitter-uses-to-deal-with-150m-active-user...
• Raffr Krikorian's Timelines at Scale : https://www.infoq.com/presentations/Twitter-Timeline-Scalability
• TAO: Facebook’s Distributed Data Store for the Social Graph : http://0b4af6cdc2f0c5998459-c0245c5c937c5dedcca3f1764ecc9b2f.r43.cf2.rackcdn.com/11730-atc13-bronson...