zit 0.3.11

zit 0.3.11 fixes a quadratic in the sync server. A pull between two peers that already hold the whole repository transfers nothing, and at 1.25M artifacts it took over seventeen minutes to do so. The server's share of that — 760 seconds of CPU — is gone: the same pull now costs the server under five seconds.

No artifact, tag namespace, sync message, or on-disk format changed.

The server no longer scans per artifact

Composing a sync reply, the server walks every artifact it holds and, for each, avoids re-announcing something the peer already has by checking the peer's announced list. That check was a linear scan of the list, run once per held artifact — and because an ordinary pull announces the peer's entire holdings, both the walk and the list were the size of the repository. The reply was O(held x announced): 9.5x the artifacts cost 78x the server CPU. It did not grow slowly; past a few million artifacts it does not complete.

The announced and requested names are now built into one set per reply and probed once per held artifact — O(held). On the 1.25M no-op pull the server's work falls from 760s to 4.9s; the whole pull, from 17.4 minutes to 4.7. The remaining time is a separate, linear cost — announcing and materialising every held artifact one at a time — which is what cluster minting will bound; it is not this fix.

Why it was never caught: the read verbs and clone were measured and level with fossil, but clone announces nothing (it converges on a record cursor), and no both-sides-full pull had ever been run at the scale where a small quadratic constant becomes minutes. The pull now carries an evidence counter — announcement probes per reply — pinned at two repository sizes to track the holdings, not the announcement; a quadratic cannot pass it. A both-sides-full incremental pull is now part of qualification.

Compatibility

• Artifacts, tags, and the sync protocol are unchanged; Fossil RFC revision 00 remains the target.
• No on-disk or cache format changed, and no wire bytes changed — the fix is the same reply computed faster.
• No command, flag, or output changed.

Qualification

zig build test, e2e, smoke (Fossil interop against a real fossil), muscle (41 differential steps), git-import-e2e, git-export-e2e, and dst, plus the three-runner CI battery (macOS ARM64, Linux x86-64, Linux ARM64). The before/after pull timings were taken on the sub-manifest pkgsrc corpus with release builds; the server's collapse from 760s to 4.9s was confirmed by stack sampling the serve process across both.