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perf(relay): cache Git pack hydration (#2169)

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thomaspblock
2026-07-20 16:50:11 +02:00
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parent 984645ecaa
commit a4d82ec722
13 changed files with 944 additions and 104 deletions
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docs/git-on-object-storage.md
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@@ -51,13 +51,19 @@ to three stated axioms, each empirically gated per backend" does.
### v1 deployment architecture
The implementation has *no per-repo persistent filesystem state*. Every request
hydrates an ephemeral working tree from the published manifest, runs the
appropriate git subprocess against it, and drops the tree on scope exit:
The implementation has *no authoritative per-repo filesystem state*. Every
request hydrates an ephemeral working tree from the published manifest, runs
the appropriate git subprocess against it, and drops the tree on scope exit:
read paths (`info/refs`, `upload-pack`) via `hydrate_for_read`, the write path
(`receive-pack`) via `hydrate_for_write`, which also returns the `ParentState`
the CAS at §Push step 7 predicates on. The relay is multi-instance-ready by
construction: nothing on local disk needs to be coordinated between instances.
Each process may retain a byte-bounded, process-lifetime cache of immutable
pack/index pairs keyed by verified digest. Deployment mounts that cache on a
per-pod ephemeral volume, so accounting and single-flight coordination stay
local. Cache misses, restarts, and evictions only affect performance; object
storage remains the source of truth, and per-request refs/HEAD are still
materialized from the current manifest.
The accepted v1 tradeoff: under concurrent same-repo pushes, every contender
hydrates and runs receive-pack, and the CAS losers' subprocess work is
@@ -475,6 +481,7 @@ symbol search, not line counts.)
| `GitStore::{put_pack, put_manifest, put_pointer}` (create-only + CAS) | `store.rs` |
| `run_conformance_probe` (A1/A3 fail-closed startup gate) | `store.rs` + `main.rs` |
| `hydrate_for_read` / `hydrate_for_write` | `hydrate.rs` |
| Bounded digest-keyed pack/index cache and single-flight population | `pack_cache.rs` |
| `ParentState { if_match, parent_digest, parent }` + `from_loaded`/`fresh` | `cas_publish.rs:154` |
| `cas_publish(.., &parent_state) -> Result<CasSuccess, CasError>` | `cas_publish.rs:410` |
| `CasError::Conflict { winner_manifest, winner_manifest_key }` (typed 412) | `cas_publish.rs:92` |