Simone
b5c18a6d70
Measured first, as thread entry #12 requires: a cold furyrs pipeline is 134.7s, target/ is 3.0 GiB raw and 2.5 GiB pruned, and the stored entry is 645 MiB. A warm job pays 8.1s (upload + extract) to skip ~120s of dependency compilation. Publishing costs 15.7s but only on a miss. Build it. The assertion in the plan turned out to be worthless and is replaced. It re-scanned for */.fingerprint/<member>-* after deleting exactly those paths, so asked to catch a planted fury-core fingerprint it exited 0 -- the prune had removed the evidence before the check looked. An assertion sharing its globs with the deletion can only prove that rm ran; it cannot see the failure that matters, which is a glob that never matched the artifact in the first place. The replacement asks a different oracle. Cargo records in each .d depfile the sources an artifact was built from: dependencies point into the registry, anything built from workspace source points back into the workspace. After a correct prune, zero surviving depfiles reference workspace source outside target/. Verified negatively too -- an artifact named totallyunrelated-abc123.d that no prune glob matches, declaring a dependency on fury-core/src/lib.rs, makes the script exit 2 and refuse to publish. zstd is already present on the template, so no rebuild is needed; the gzip fallback stays for the plain LinuxBuild2404.
4.1 KiB
Cargo dependency cache — measurements
Measured 2026-07-22 on a LinuxRust2404 linked clone (4 vCPU, 3.9 GB RAM,
rustc 1.97.1, zstd present at /usr/bin/zstd), running furyrs b8ea567
with the build-command block from its .gitea/workflows/ci.yml verbatim.
Entry #12 of the furyrs thread set the rule: measure before building. There it killed the registry cache — 9.3s of saving for +800 MB on the template. Here the numbers point the other way, decisively.
Baseline
Cold pipeline, empty target/ |
134.7s |
Matches the 133s furyrs reported for job 1021 and the 126.6s measured in #12, so the clone is representative.
Sizes
| Bytes | Human | |
|---|---|---|
target/ raw |
3,206,670,175 | 3.0 GiB |
tar of raw target/ |
3,215,503,360 | 3.0 GiB |
tar + zstd -3 -T0, raw |
810,108,028 | 773 MiB |
target/ after prune |
2,719,971,105 | 2.5 GiB |
entry as stored (tar --zstd, pruned) |
676,585,779 | 645 MiB |
Pruning strips 487 MB (15%) of raw target/, which is the workspace crates'
own artifacts — 42 fingerprint directories across the six members
(fury-core 11, fury-gui 12, fury-ipc 6, fury-backend 5, fury-cli 5,
furyd 3). 1,928 dependency artifacts and 903 dependency fingerprints survive.
Costs
| Step | Seconds | Paid by |
|---|---|---|
| prune + assert | 0.21 | publish |
pack (tar --zstd) |
10.88 | publish |
| fetch guest→host (140 MiB/s) | 4.62 | publish |
| publish total | 15.7 | only on a cache miss |
| upload host→guest (179 MiB/s) | 3.60 | restore |
| extract | 4.52 | restore |
| restore total | 8.1 | every warm job |
Verdict: build it
A warm job pays 8.1s to skip roughly 120s of dependency compilation —
the ~490 external crates that a committed Cargo.lock keeps bit-identical
between runs. Net saving ≈ 112s on a 134.7s job, about 83%.
The publish path costs 15.7s but runs only on a miss, i.e. once per
Cargo.lock change, so it is amortised across every run in between.
Transfer is not the bottleneck anyone feared: the virtual NIC moves the entry at 140–180 MiB/s, so 645 MiB crosses in under 4 seconds each way.
Notes that changed the implementation
zstd is already in the template. /usr/bin/zstd is present on
LinuxRust2404, so the gzip fallback is dead code in practice and no template
rebuild is needed. Keep the fallback anyway — it costs one branch and keeps the
feature working on a plain LinuxBuild2404.
The name-based assertion was worthless and was replaced. The plan's
original check re-scanned for */.fingerprint/<member>-* after deleting
exactly those paths. Asked to catch a planted fury-core-deadbeefcafe
fingerprint, it exited 0 — the prune had deleted the evidence before the
assertion looked. An assertion built from the same globs as the deletion can
only prove that rm ran; it is blind to the failure that matters, a glob that
never matched the artifact at all.
The replacement asks a different oracle. Cargo records in each .d depfile the
source files an artifact was built from: a dependency points into
/opt/rust/cargo/registry/..., anything built from workspace source points
back into the workspace. After a correct prune, zero surviving depfiles
reference workspace source outside target/. Verified negatively as well — an
artifact named totallyunrelated-abc123.d (which no prune glob matches)
declaring a dependency on fury-core/src/lib.rs makes the script exit 2
and refuse to publish.
| Check | Clean tree | Planted fingerprint | Planted foreign artifact |
|---|---|---|---|
| name-based (original) | 0 | 0 — missed it | 0 — missed it |
| depfile-based (shipped) | 0 | 0 (prune removed it, correctly) | 2 — refused |
Feature variants coexist in one entry, as predicted. deps/ holds
libclap-943062c20e623534.rmeta and libclap-abe395d6778d44ce.rmeta side by
side — the same crate compiled under two different feature resolutions. This is
why the feature set is not part of the cache key: cargo already separates the
variants by hash, so one entry serves all of furyrs's four feature
configurations instead of fragmenting into four.