Logan: A High‑Performance Mobile Logging Library for Meituan‑Dianping

Background

For mobile applications, a logging library is an essential infrastructure. Meituan‑Dianping’s mobile apps generate tens of billions of log entries daily. To address common issues such as efficiency, security, and log loss, the Logan basic logging library was created.

Existing Problems

Typical mobile logging libraries suffer from:

Performance stutter caused by frequent heap allocations and GC.

Log loss when the app crashes before logs are flushed.

Insufficient security – logs may be exposed in plain text.

Fragmented logs across different types (end‑to‑end, code, crash, analytics) making troubleshooting costly.

At the scale of Meituan‑Dianping, these problems are amplified, leading to unstable and unusable logging modules.

Introduction

Logan (Log + An) is Meituan‑Dianping’s native mobile logging library. It stores various log types locally, supports retrieval and analysis, and is integrated with many internal log systems.

Design

Performance Stutter

Logging involves heavy I/O, which can cause GC pauses and CPU spikes. Logan moves the core logic to a native C library, enabling:

Memory‑only caching to avoid Java heap pressure.

Streaming compression and encryption to reduce CPU peaks.

Cross‑platform support for Android and iOS.

Log Loss

Logan uses an MMAP‑based mechanism. MMAP maps a file into the process address space, allowing memory‑like operations on disk. Benefits include:

Fast, memory‑speed access to the log file.

OS‑controlled write‑back, reducing loss on abrupt termination.

Reduced copy operations, improving I/O efficiency.

If MMAP initialization fails (≈0.002% of cases), Logan falls back to heap‑based caching.

Security

Log files are encrypted using a symmetric key. When uploading, the symmetric key itself is encrypted with an asymmetric key, preventing plain‑text exposure and protecting logs in transit.

Log Fragmentation

Logan defines a custom log protocol that normalizes different log types into a unified format, stores them locally, and aggregates them for centralized display. The platform provides timeline and detail views to help developers locate issues quickly.

Architecture

The overall architecture includes a native C core, a custom log protocol, MMAP for caching, AES encryption, and APIs for proactive reporting.

Log Fragmentation

Logan splits oversized logs into 20 KB fragments, stores each fragment according to the protocol, and reassembles them on the backend.

Log Writing Flow

Performance Evaluation

Benchmarks comparing Java‑based logging with Logan’s C implementation show:

Java: frequent GC pauses.

C: no GC, smoother memory usage.

CPU usage is also lower for the C version because streaming compression/encryption avoids peak loads.

Featured Functions

Log Retrieval

Using Meituan‑Dianping’s PushSDK, Logan can pull local logs from a device after a retrieval command, respecting network type and size limits to save mobile data.

Proactive Reporting

Instead of relying on Push, apps can actively invoke an upload API, bypassing push‑related delays and ensuring logs are sent before user complaints arise.

Online Impact

Since its launch in September 2017, Logan has been stable and significantly improved engineers’ ability to analyze logs and locate issues.

Logan now serves many log types (CAT end‑to‑end, analytics, code, network, push, crash, etc.) across Meituan, Dianping, Meituan Waimai, Maoyan, and other apps.

Future Outlook

H5 SDK

Currently only native Android/iOS versions exist. An H5 SDK is planned to bring the same protocol and aggregation capabilities to pure JavaScript pages.

Log Analysis

Future work includes automated machine analysis of logs to surface key paths, risk detection, and malicious request identification.

Authors

Baifan – Android technology expert, responsible for Logan SDK development and promotion.

Licheng – Senior Android engineer with experience in cross‑platform development and mobile testing.

Recruitment

The Meituan‑Dianping mobile R&D center in Shanghai continuously seeks engineers focused on mobile infrastructure. Contact: hui.zhou#dianping.com.