Optimizing Feed and Follow Systems in Firestore

Scalability Issues with Realtime Database

In your previous social network app using Firebase Realtime Database, you faced scalability issues due to the following:

• Posts were added to the timelines of all followers, even for a user with numerous followers.
• New followers received all the previously posted content of the users they followed.

Optimized Firestore Structure

To resolve these issues in Firestore, consider the following database structure:

• Three top-level collections for users, following, and posts.
• Users have documents with fields like name and email.
• The following collection contains documents for each user, with sub-collections for the UIDs of users they follow.
• The posts collection contains documents for each user, with sub-collections for the Post IDs of their posts.

Improved Scalability

This structure allows for efficient handling of followers and posts:

• Storing followers in sub-collections eliminates the need to copy data.
• Separating posts into sub-collections ensures that retrieving the latest posts of followed users remains performant, even with a large number of followers.

Querying for Followed User Posts

To display the latest posts in the feed of a user, you can use the following query:

Query query = rootRef.collection("posts/"   uid   "/userPosts")
    .orderBy("date", Query.Direction.DESCENDING).limit(3);

This query retrieves the latest three posts for the specified user (uid) and can be utilized in a paginated manner for continuous loading.

Optimization for Large Post Volume

To optimize handling of large post volumes, consider storing the posts that should be displayed in a user's feed in a separate document or sub-collection for that user. This ensures efficient retrieval and avoids the issue of new followers receiving all previously posted content.