AI BriefingGitHub moves busiest Git repos to Azure with per-reference write serialization
·2026.10.22 01:00
Key point
The change decouples write locks from the whole repository to individual references, allowing concurrent writes to different branches despite cross-region latency.
Details
- GitHub migrated 99.99999% of repositories to a dual-region setup spanning its own data centers and Azure, with Azure now serving about half of Git traffic.
- The remaining 0.00001% of busiest repositories were held back by a 25ms round-trip latency that serialized writes across regions, creating a throughput bottleneck.
- GitHub changed the quorum scope from repository-wide to per-reference, allowing writes to different references to proceed in parallel; internal testing showed 3-4x higher write throughput at lower latency.
- A new "virtual write replica" was introduced to stream writes to Azure Blob Storage, enabling the decoupling of read and write compute for independent scaling.
- This architecture supports the "agentic shift" by providing headroom for rapidly growing traffic without waiting for a full architectural overhaul.
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