HTTP3/QUIC Upgrade and Performance Improvements in Taobao's Long‑Chain Network

The article describes Taobao's large‑scale migration of its long‑chain network to HTTP3/QUIC using the internally developed XQUIC library. After years of using a private SlightSSL protocol on HTTP/2, the team introduced a full HTTP3/QUIC stack to address handshake latency, improve network reliability, and provide a reusable solution for multiple business scenarios such as recommendation, transaction, upload, and short‑video.

Taobao's TNET library, which serves over 90% of the platform's HTTPS traffic, now abstracts protocol differences and offers unified interfaces for HTTP2, HTTP3, custom tunnels, DNS, traceroute, MTU detection, and ICMP probing. The upgrade includes client‑side policy fetching, UDP connectivity probing, and fallback mechanisms to ensure seamless operation across diverse network conditions.

Performance measurements show significant reductions in latency and improvements in success rates: recommendation latency decreased by up to 33% (P99), transaction latency by 32%, upload speed increased by up to 21%, and short‑video download speed improved by 18%. Additional gains were achieved by optimizing UDP traversal, 0‑RTT usage, and protocol‑specific encryption handling.

Operational challenges such as UDP port rebind, five‑tuple forwarding limitations, and kernel‑level UDP memory constraints were addressed through UDP probing, CID‑based load balancing, kernel upgrades, and socket options. The following code snippet illustrates the socket option used to enable UDP hash optimization: setsockopt(s, SOL_UDP, 200, (const void *) &value, sizeof(int))