Full Volume Message Push Implementation Based on Public Mailbox at Baidu

This article introduces Baidu's implementation of full volume message push notifications using a public mailbox mechanism. The background stems from Baidu App's need to reach all 600M+ monthly active users with low user disturbance, particularly for scenarios like pandemic policy dissemination.

The article first explains the existing IM system architecture, including user entities, accounts, relationships, chat sessions, and messages. It describes the notify-pull pattern where real-time notifications trigger message pulling from the server, and introduces the user mailbox system (private mailbox, group mailbox) for offline message storage.

Three implementation approaches are compared: (1) Push through notification entry to all users' private mailboxes; (2) Skip notification entry and write directly to mailboxes; (3) Public mailbox mechanism using read diffusion. The third approach stores messages in a single public mailbox and merges it with user private mailboxes during message retrieval, trading read cost (CPU) for write cost (storage).

The implementation includes: full message management workflow (O-end operations, access layer, logic layer, mailbox proxy, storage layer), user mailbox pulling with public mailbox memory caching (4.7Wqps peak), and a graded release mechanism with whitelist support.

Advantages include fast distribution speed and low resource cost. Limitations include unsuitability for high personalization scenarios and real-time notification scenarios due to system pressure concerns.

During Q4 2022 pandemic reopening, three full volume messages were successfully delivered to 200M+ users each within 3 days, demonstrating the system's effectiveness.