GitHub scales Git storage with per-reference quorum
- Most GitHub repositories now keep two of their five replicas in Azure, which handles about half of Git traffic.
- GitHub narrowed write serialization from an entire repository to individual references; in internal tests, writes to different references achieved 3–4x higher throughput with lower latency.
- Azure Blob Storage now participates in the quorum through a virtual write replica, and a write is acknowledged only after it is durable in object storage.
- GitHub can add virtual read replicas on demand; they load cache data from Azure Blob Storage and reconcile their local state in the background without joining the quorum.
Our take
For agents or developers pushing separate branches, per-reference ordering avoids the old repository-wide write lock; writes targeting the same reference still contend. Detaching read replicas from the quorum allows read capacity to scale separately, but background reconciliation does not yet support every read workload, so some reads need an in-line catch-up path. The quorum remains the constraint on further write scaling, leaving ordering and durable reference state as unresolved engineering work.
Sources
- The bridge to agent-scale Git infrastructure · GitHub Blog
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