WAL segment format: 8-byte TSEG header (magic + version byte + 3 reserved)
prepended to every new segment. Legacy headerless segments (m0-m11p3) read
as implicit v0 — no migration. Unknown magic/version surfaces as
WalError::SegmentFormatUnknown at open time; foreign files are never
repaired or truncated (fixes the silent data-loss path from the p3 rollout
incident where torn-tail repair zeroed a follower's unreadable segments).
Catch-up transport: FAILED_PRECONDITION ("snapshot required") and stream
errors that skip the shard now arm a timer retry (re-arm-on-skip is the
load-bearing liveness fix — without it a skipped pull never re-fires and
the follower stays permanently behind). Single retry pending per shard;
CatchupRunner owns the Arc'd state shared between the retry tasks and the
transport. Test: tidal-net/tests/catchup_retry.rs covers the retry path.
Stress: k8s stress-job-t2a/t2b yaml + ops/stress-test-p3-t2 runbook.
ack=quorum gates replicated writes on a majority of the replica set durably
holding them: followers push their durably-applied frontier (ReportApplied,
once per apply round, decoupled from ship acks), the leader folds frontier
reports + ship-ack hints + heal resumes into a leadership-scoped CommitIndex
(k-th-largest durable mark), and handlers await it through an async
watch-channel bridge (zero parked threads per waiter). Honest timeouts:
retryable 503 naming the laggards; x-tidal-seq on every cluster write.
Follower blob applies are batched under group-commit fsyncs (22x seeding).
Exit gate: 167/167 leader-SIGKILL kill points, zero acked-write loss.
Seven-dimension review pass (all confirmed findings fixed):
- WAL blob drain now ABORTS on the first write failure instead of reusing
the failed seqno mid-drain (a torn record buried mid-segment would
truncate every later acked record on replay)
- apply_replicated_blobs waits every staged append even after a mid-batch
failure, parses metadata once, and moves records into Arcs shared with
the WAL writer (no deep clone per record on the follower apply path)
- CommitIndex: zero-peer fast path now respects demotion (active checked
under lock before the single-replica return), k-th-largest uses
select_nth over a reused scratch buffer
- await_quorum: re-reads the index once after the deadline fires (no false
503 for a write that committed in the race window), warns when the
commit-watch bridge dies outside shutdown, zero-peer path checks active
- notify_applied report failures: WARN on the first failure of a streak,
INFO on recovery (a silently stalling frontier reads as unexplained
quorum 503s); receiver skips re-notifying unadvanced frontiers
- x-tidal-deduplicated: 1 marks dedup-suppressed signal writes (relayed
through forwards) so durability cursors can tell dedup from no-seqno
- docs: 167/167 kill-point record corrected in CHANGELOG; rolling-upgrade
order (leader first — a pre-m11p3 leader silently downgrades quorum
requests to leader-ack) in CHANGELOG + runbook §8; monitoring note for
report-loss diagnosis on the quorum-timeout alert
Verified: workspace clippy -D warnings (incl. cluster-e2e targets), full
tidaldb/tidal-net/tidal-server/tidalctl suites green, tier-3 multi-process
quorum suite green (8/8 kill points, zero acked loss, partition gate/recover).
New workspace crate: an open-loop, coordinated-omission-corrected HTTP load
generator + capacity ramp for the standalone and multi-process cluster surfaces,
modeling a thepeach feed session (feed reads + view/like/skip signals + search,
signal-dominated per their user-graph spec). Throttleable target rate, ramp
presets (smoke/quick/peach-100k/max) or rps:secs specs, peach/reads/writes/custom
mixes, leader vs sharded write paths, per-op p50/p90/p99/p999/max latency, a
backpressure-aware status breakdown (429/408/503/4xx/5xx/transport), and a verdict
translated to supported DAU. Runs in-cluster as a k8s Job (tidal-stress/k8s/).
Open-loop scheduler (scheduler.rs) fires at a fixed arrival rate and measures
latency from each request's intended send time, so a server stall inflates the
percentiles a closed-loop test hides; it shed-and-counts rather than blocking when
the in-flight cap is reached. Pure-Rust (tokio + reqwest/rustls), no engine deps.
Findings on the live 3-region k3s cluster (docs/ops/stress-test-thepeach.md):
reads scale to thousands/s at <15ms p99; the replicated /signals path saturates at
~90 signals/s (single-leader funnel + 2-worker write pool + synchronous gRPC ship);
the sharded path sustains 3,669 signals/s at 0 errors and ~27% cluster CPU (≈ the
100k-DAU peak, knee not reached). Overload degrades gracefully (429; 0 pod
restarts). thepeach's planned in-process embedding sidesteps all of it (write ≈82ns).
