ci: delete the cache generations nothing can restore - #537
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The repository sits at 9.63 GB of a 10 GB Actions cache quota, and 5.58 GB of that is unreachable. Swatinem/rust-cache hashes the workspace manifests into its key and matches that key exactly — it ships no restore-keys fallback on purpose, a partially stale Rust cache being worse than none. So every merge to main that touches a Cargo.toml, the lockfile or rust-toolchain.toml mints a new generation of about 2.8 GB across the Linux, Windows and CodeQL entries, and no future run will ever derive the key of the one it replaced. Three such merges landed within nine hours (#534, #531, #536), leaving three live generations. The cleanup workflow did not touch them: its rule drops caches on main unread for seven days, and all three had been read within the hour, because every pull request restores the newest — which says nothing about the two behind it. Age is the wrong predicate. What makes a cache dead here is structural: a newer cache exists whose key shares its prefix. scripts/prune-superseded-caches.py groups by key-minus-trailing-hashes, keeps the newest of each group and names the rest. It reads a listing on stdin and writes ids on stdout, deleting nothing itself, which lets --self-test cover the whole decision — worth having, since the workflow deletes what the script prints and a grouping bug would be destructive rather than merely wrong. Ten assertions pin the parts that would hurt: that jobs and operating systems never pool, that word-suffixed job keys like linux-test-appimage are not mistaken for hashes, and that input order does not decide what survives. Run against the real listing it names six caches, 5584 MB, sparing the current generation of each group and the bun cache. It runs when a new generation appears — CI or CodeQL finishing on main — rather than only weekly, so the replaced generation does not stand for up to seven days. The age rule stays as a backstop for a group that can never shrink, where a renamed or removed job left a lone cache nothing supersedes. Measured while diagnosing this, and worth recording because the issue assumed otherwise: the restore itself works. #536 changed no manifest and hit main's entry in full — 1797 MB, "full match: true", job in 6 min 57 rather than 13 min. The misses in the report belonged to pull requests that did change a manifest, which is by design. Noted in CONTRIBUTING so the cost reads as expected rather than broken. Refs #535
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Limit details: You’ve used all 2 included reviews currently available. Your 85 included PR review attempts over the past 7 days set your current allowance at 2 reviews per hour. 📝 WalkthroughWalkthroughLe PR ajoute un pruner de caches GitHub Actions. Le workflow l’exécute après CI ou CodeQL, ainsi que manuellement. Il récupère les caches de ChangesNettoyage des caches
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: 🟡 Moderate · up to The cleanup may delete a cache generation that remains restorable under a distinct version, discarding usable build data and causing avoidable cache misses or longer CI runs. This bounded CI reliability risk remains unresolved and should be addressed or explicitly accepted before merge. Sequence Diagram(s)sequenceDiagram
participant GitHubActions
participant CacheCleanup
participant PruneSupersededCaches
GitHubActions->>CacheCleanup: Déclenche workflow_run ou workflow_dispatch
CacheCleanup->>GitHubActions: Récupère les caches paginés de main
CacheCleanup->>PruneSupersededCaches: Envoie la liste JSON
PruneSupersededCaches-->>CacheCleanup: Retourne les identifiants obsolètes
CacheCleanup->>GitHubActions: Supprime les caches obsolètes
CacheCleanup->>GitHubActions: Exécute cleanup-stale
🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches📝 Generate docstrings
🧪 Generate unit tests (beta)
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In @.github/workflows/cache-cleanup.yml:
- Around line 74-76: Update the cache collection step around gh cache list to
retrieve all caches on the main branch via REST pagination instead of limiting
results to 200, and convert the paginated response fields to the format expected
by scripts/prune-superseded-caches.py. Preserve the existing caches.json input
and pruning flow.
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.github/workflows/cache-cleanup.ymlCONTRIBUTING.mdscripts/prune-superseded-caches.py
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Review finding, and a fair one: gh cache list --limit 200 silently truncates. Reaching 200 caches on main is implausible under a 10 GB quota when the entries run 170 MB to 1.8 GB, but the failure mode is what makes it worth closing — pruning a truncated listing leaves the quota full for a reason nothing logs. Both jobs now read the REST endpoint with --paginate, which has no cap. The two flags do not compose the same way in each: gh rejects --slurp alongside --jq, so the pruner slurps the pages whole and the stale job runs its query per page and lets the matches concatenate. Verified both against the live repository — the stale filter returns nothing at the real cutoff and all ten ids at a cutoff set to tomorrow, across four pages. The pruner takes the paginated shape rather than a jq incantation converting it: entries() flattens pages and accepts REST's snake_case beside gh's camelCase. Normalising in the script keeps it under --self-test, where five new assertions cover it, one of them pinning that a generation split across a page boundary is still seen. Both listing shapes produce the same six ids against the live repository. Also switched the stale cutoff to an explicit Z suffix. --iso-8601 emits +00:00, which does not compare as a string against the API's Z — harmless at seven-day granularity, wrong at the boundary, and free to fix while rewriting the line.
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Inline comments:
In `@scripts/prune-superseded-caches.py`:
- Around line 84-90: Update the cache normalization in entries() to retain the
API-provided version field, then make superseded() group caches by both
group_of(cache["key"]) and cache["version"] so distinct versions are never
treated as interchangeable. Add coverage demonstrating that two caches with the
same key group but different versions are preserved independently.
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Running the purge by hand against the live repository turned every delete into "already gone", and the step would have reported a clean run. The listing was written on Windows, so each id reached gh with a trailing carriage return and matched nothing. The ids were fine; the tolerance was too wide. That tolerance exists for a real case — GitHub evicts on its own to hold the quota, so a cache can vanish between the listing and the delete, and one failure is a lost race rather than a fault. But every one failing is a different animal: the ids are malformed or the command is wrong, and swallowing that leaves the quota full while the job reports success. So the step now counts both outcomes, prints them, and fails when it deleted nothing and lost every id. CRLF cannot happen on ubuntu-latest, where python3 writes LF. The guard is not for that bug, it is for the class: a systematic failure that the per-id tolerance would render invisible. Verified by extracting the step body from the YAML and running it under a stubbed gh: six deleted exits 0, five deleted with one vanished exits 0, and all six failing prints the ::error:: and exits 1. The purge itself ran: 11 caches and 8.97 GB down to 5 and 3.52 GB, leaving the current generation of each job, the bun cache and #486's.
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Purge exécutée à la main contre le dépôt, via le pipeline exact du workflow — 11 caches / 8,97 Go → 5 caches / 3,52 Go, 5,58 Go libérés. Restent la génération courante de chacun des trois jobs, le cache Elle a aussi trouvé un trou que la revue n'avait pas vu. Tous les Cette tolérance a une vraie raison d'être — GitHub évince tout seul pour tenir le quota, donc un cache peut disparaître entre le listing et la suppression, et un échec isolé est une course perdue. Mais tous échouer est autre chose : ids malformés ou commande fausse, et l'avaler laisse le quota plein pendant que le job se déclare vert. Le CRLF ne peut pas se produire sur Vérifié en extrayant le corps de l'étape depuis le YAML et en l'exécutant sur un |
Review finding, and it holds. A restore matches key and version, so two versions under one prefix are not interchangeable — version hashes the cache paths, and an entry under a different one answers a question the newer entry cannot. Grouping on the prefix alone could therefore delete something a run would still reach, which contradicts the only claim the script makes. The concrete shape is two jobs sharing a job id and an operating system but caching different paths: each run would evict the other's entry, and neither would ever hit again. Nothing in this repository splits a prefix that way — the five live groups each hold exactly one version, and the three Linux rust-cache groups even share it, since `src-tauri` and `src-tauri -> target` resolve to the same paths. The pairing is what keeps the rule honest rather than something the current tree needs. It costs a little reach in the other direction: a version that really did die, because the paths changed and nothing derives it any more, now survives this rule. It falls to the seven-day age backstop instead, so the staleness is bounded rather than permanent — the right side to err on, given the rule's justification is reachability. Version is absent from a listing that did not ask for it, in which case every entry gets the same blank and the grouping degrades to today's behaviour rather than fragmenting. Four assertions added, including the one the finding asked for: two caches sharing a key group under different versions are both preserved, and within one version the newest still wins. Verified against the real pre-purge snapshot — the same six ids, unchanged.
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Closes #535.
The measurement the issue asked for
The issue held two candidate causes apart and said which of them
dominates "is not established". It is now.
The restore works. #536 changed no manifest, and its
Rust (ubuntu-latest)run restoredmain's entry in full:Job total 6 min 57 rather than 13 min, and the post step logged
Cache up-to-date— no save. The 1–2 s restores in the report belongedto #534 and #531, both of which did change a manifest. So the
key-per-manifest miss is real and by design, and there is nothing to fix
in the restore path. That expectation is now written down in
CONTRIBUTING.md, so a 13-minute job on a lockfile bump reads as thecost of the change rather than a broken cache.
The quota is a separate problem, and it is the one worth fixing.
What is actually filling the quota
gh api …/actions/cache/usage→ 9.63 GB of 10 GB, and 5.58 GB of itis unreachable. Three merges inside nine hours each touched a cache-key
input, and each minted a whole generation:
rust-toolchain.toml(#534)2e9a1d04Cargo.toml(#531)f884c40frust-toolchain.toml(#536)6da14145Only the last row is reachable.
Swatinem/rust-cachematches its keyexactly and ships no
restore-keysfallback, so no future run will everderive a key from the first two rows again.
cleanup-staledid not touch them, and could not have: it drops cachesunread for seven days, and all three had been read within the hour —
every pull request restores the newest one, which refreshes nothing
about the two behind it. Age is the wrong predicate. What makes a
cache dead here is structural: a newer cache exists whose key shares its
prefix.
The change
scripts/prune-superseded-caches.pygroups by key-minus-trailing-hashes,keeps the newest of each group, names the rest. It reads a listing on
stdin and writes ids on stdout — no deletion, no network call — which is
what lets
--self-testcover the entire decision. Worth having, becausethe workflow deletes what the script prints: a grouping bug here is
destructive, not merely wrong. Ten assertions pin the parts that would
hurt — that jobs and operating systems never pool, that word-suffixed
keys like
linux-test-appimageare not mistaken for hashes, that inputorder does not decide what survives.
The workflow now also fires when a generation appears (CI or CodeQL
finishing on
main), not only weekly, so a replaced generation does notstand for up to seven days.
cleanup-stalestays as the backstop forthe one case the new rule cannot reach: a renamed or removed job leaving
a lone cache nothing supersedes.
Not adding
save-if: main only, the issue's first option. It would freethe ~678 MB a single open pull request holds, at the cost of every
pull request rebuilding from scratch on each push. With the superseded
generations gone the repository sits near 3 GB, so there is no reason to
buy space with iteration speed.
Verification
--self-test→ 10 assertions pass, and it runs in the workflow beforethe real listing is ever piped in.
sparing the current generation of each group and the
buncache.python3 scripts/check-toolchain-pin.pystill passes on the new tree.workflow_run,scheduleandworkflow_dispatchonly fire from thedefault branch. First real run is after merge;
workflow_dispatchisthere to trigger it on demand rather than waiting.
Summary by CodeRabbit
Nouvelles fonctionnalités
Documentation