The details of what exactly is important for the purpose of determining the "other post" can significantly impact how you need to store the data and the perform

The details of what exactly is important for the purpose of determining the "other post" can significantly impact how you need to store the data and the performance implications of doing so. Does it depend on the time the request is made or just based on the data in the database? Can you determine approximately when that other post is likely to change or do you have to try to compute it on every request? Is the "other post" the same for all the users? For a subset of users? Is it unique for every user?