How can Firestore optimize feed and follow systems for scalability in social networks?

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:

<code class="java">Query query = rootRef.collection("posts/" + uid + "/userPosts")
    .orderBy("date", Query.Direction.DESCENDING).limit(3);</code>

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.

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