Is it always necessary to use foreign keys?

Question

PostgreSQL

Is there a performance benefit if using foreign keys in postgresql?
I understand that foreign keys are mostly for data integrity, but doesn't this slow down the process at large volumes?
After reading an article about the architecture of Instagram, I focused on the proposal: Decided to vertically split the data into several databases, using the routers mechanism from the ORM, getting rid of foreign keys in parallel
Simple task: there is a table of users and a table of posts. The posts table has a user_id field . There are a lot of posts. Should I make a foreign key and link the posts table to the users table or just put an index on the user_id fieldand achieve maximum performance?

Answer 1

Is there a performance benefit if using foreign keys in postgresql?
Apparently it meant whether there is a performance gain if NOT using foreign keys. Yes, may be. First, the foreign key check itself is not free - it's a system-level trigger. Second, postgres takes (among other things) a SHARED lock per row in the parent table. Accordingly, you need to take into account the impact of this on performance and monitor deadlocks.
However, here's a practical tip for you - leave these keys for now, postgres is very fast even with them, and a very big question is whether it is worth sacrificing data integrity for the sake of some (perhaps insignificant) performance gain (and without keys, your data is guaranteed to disperse).

Answer 2

Foreign keys are not used in highload: integrity control at the storage level is not possible there.
If there is an opportunity to use them, then they should be used.