How Does Facebook Track Notification Read Status in Its Database?

Database Design for Facebook-like Notification Tracking

In this article, we delve into the database structure behind Facebook's efficient notification tracking system. While complexity is not the focus here, we will explore a simplified table structure that ensures effective tracking of notifications and their read status.

Facebook's notification database typically includes a table called notifications with fields such as id, userid, update, and time. This table provides a centralized repository for storing and managing user notifications.

However, to track which notifications have been read and unread, a separate table called notificationsRead is often introduced. This table includes fields such as id, lasttime_read, userid, and potentially other attributes.

The last time read field in the notificationsRead table acts as a reference point for determining which notifications a user has viewed. To retrieve unread notifications, the query would typically compare the time field in the notifications table with the lasttime_read field in the notificationsRead table for a given user. Only notifications with a time greater than the lasttime_read value would be considered unread.

Here is an example query for retrieving unread notifications:

<code class="sql">SELECT `userid`, `update`, `time`
FROM `notifications`
WHERE
`userid` IN (... query to get a list of friends ...)
AND
(`notifications`.`time` > (
    SELECT `notificationsRead`.`lasttime_read`
    FROM `notificationsRead`
    WHERE `notificationsRead`.`userid` = ...$userid...))</code>

This approach provides an efficient and scalable method for tracking Facebook-like notifications, both for read and unread statuses, within separate tables. This separation allows for efficient filtering and retrieval of specific types of notifications.

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