I have a newsfeed with comments. I’m storing comments in MongoDB. Newsfeed possibly could grow very large in future so I need high speed.
comments: [
{user_id: 34, user_name: "John", text: "..."}
]
As you can see, I’m storing info about user as well because Mongo’s docs say “when you need speed, use embeds”.
But user can change his name anytime.
In that case user’s name under each of his comments in newsfeed would be wrong.
Should I use references (DBref) to “User” collection by _id instead of embeds? And how much slower would it be? Is that slowdown big enough to be worried about it?
I’m just wondering how all big social networks are doing that. When I change my user’s name it instantly updates in all my posts in newsfeed.
Storing DBRefs won’t gain you any benefit vs. storing simple user ids. It’s basically the same id, only with a collection name.
If you want quick efficient reads – embed.
When user changes his name, you can write this fact down and then run a nightly job that’ll update his cached name in all comments.
If you want instantaneous name updates – you should reference. But in this case you’re paying with more complex code and more queries to the database.