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Krzysztof kuhy Rudnicki
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Renames this repo's markdown onto README.md / CLAUDE*.md / DOCS*.md / TODO*.md so a future session can tell a live task from a finished record without reading the file to find out. TODO files carry the literal "REMOVE ME AFTER FINISH" and are deleted when the work lands. Enforced by the md-naming pre-commit hook and CI workflow, both delegating to the shared gate in kuhyx/utils so this repo's idea of a valid name cannot drift from every other repo's. Includes the patch bump this repo's bump-patch-version hook applies to app/pubspec.yaml on every commit. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01A47aX5DJwmA3QFn3pkEWi7
99 lines
4.7 KiB
Markdown
99 lines
4.7 KiB
Markdown
# Sync latency: what must never block the user
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Measured 2026-08-21 against the live remote. Before this work the gate ran a
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*full* sync tick before deciding whether to lock: ~27s, and the lock screen's
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"Fetch from sync" button ran the same tick inline on the Tk thread.
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| Path | Before | After |
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|---|---|---|
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| `gate --check` (nothing due) | 216ms | ~105ms |
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| "Fetch from sync" button | 18-27s | ~84ms |
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| `diet-guard log ...` | 15.5s | ~2ms |
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| Background full tick | ~27s | ~8.9s |
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## The narrow pull
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`_sync_refresh.pull_peer_logs()` answers one question — *"has a peer already
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logged this slot?"* — and only the peer **logs** can answer it. No budget, no
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food banks, no `rebuild_food_bank`, and **no push**.
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Three state invariants, each with a regression test, because each is silent
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when broken:
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* **`pushed_rev` survives verbatim.** This pass never pushes; overwriting it
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convinces the next full tick it has already published, and the device goes
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invisible to every peer, permanently.
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* **`peer_revs` is merged, not replaced.** Only changed peers are visited, so a
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wholesale replace drops every untouched entry and re-downloads them next tick.
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* **The log is written before the state.** The other order records a peer as
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merged while its records are absent — silent data loss.
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Peer enumeration deliberately avoids `list_directory` (~445ms mirrored, because
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the GitHub half alone is ~360ms) and unions the revision map with `peer_revs`
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instead. Membership is tested with `in`, never `.get(...) is not None`:
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`peer_revs` legitimately holds explicit nulls, and treating those as "never
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seen" re-downloads them forever.
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## Threading
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The fetch button runs the pull on a **daemon** worker and marshals the result
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back through a `queue.Queue` polled by `root.after`. The worker touches **no
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widget** — Tcl is not thread-safe, and that includes `after`. Polling also
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makes the completion path testable with no thread at all: put a result on the
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queue, call the poll, assert.
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A second click while a fetch is in flight is ignored. That is the reentrancy
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guard *and* the write-race fix: the pull persists its merge, so two workers
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would race two `write_raw_log` calls and orphan one result.
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`diet-guard log` publishes through `publish_after_log_detached` (non-daemon, so
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the process waits for the push at exit while the user already has their
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output). **The gate does not**: `diet-guard-gate.service` is `Type=oneshot`, so
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systemd reaps the unit the moment the main thread exits and a background push
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would be killed halfway.
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## Timeouts
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`INTERACTIVE_TIMEOUT_SECONDS` (2s) bounds anything a user waits on.
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`SYNC_TIMEOUT_SECONDS` (10s) only ever reached GitHub: `firebase_client_for`
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accepts no timeout in crdt_sync v0.6.0, so Firebase silently used its 15s
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default and one hung session refresh stalled the lock window. The journal
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recorded five such failures in five days, one of them a meal that logged
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locally and never published.
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`_apply_timeout` reaches for the private `_timeout_seconds` because the pinned
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library exposes no other lever. The clean fix is a `timeout_seconds` kwarg
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upstream; that is a cross-repo change (five consumers, tag bump).
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## Stale peers
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Every install mints a uuid and pushes under it, and nothing cleaned them up.
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This remote reached 25 devices. Each dead one cost a round trip in the log pull
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and in each of the three bank syncs — roughly 400ms per peer per tick.
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They were not phone reinstalls: seventeen were frozen at the *same* instant
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(2026-08-13T16:45:04) holding near-identical ~400-record copies of one log,
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the signature of repeated fresh-install runs. 20 were pruned on 2026-08-21
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after verifying zero records would be lost.
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`prune-peers` is dry-run by default, refuses `--apply` without `--backup-dir`,
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and never proposes `pc`/`phone`/`desktop` (they carry pre-migration history and
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`SYNC_LEGACY_DEVICE_ID` names one as this device's own former path).
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**It must delete each device's `revs/` marker along with its data.**
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`_candidate_peers` enumerates peers from that map rather than from
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`list_directory`, so an orphaned marker resurrects a deleted device as a
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candidate and buys a round trip discovering it is gone. Pruning without this
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took the narrow pull from ~90ms to ~15s — slower than before the prune.
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## Import cost
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`gate --check` used to import `requests` (~78ms) and tkinter for a window it
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never opens. Both are now resolved through module-level `__getattr__`
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(PEP 562) plus `import_module`, which keeps every existing `patch.object`
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target working and needs no lint suppression. The chains were
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`_cli_args` -> `_cli_sync` -> `crdt_sync` -> `requests`, and
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`_cli_log` -> `_resolve` -> `_estimator_off` -> `requests`.
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Verify with `python -X importtime -c "import diet_guard._cli_gate" | grep -c requests` (expect 0).
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