Both playlists shared one hash and sorted set, causing two independent
failures.
Starvation: Snapshot performed an unbounded ZRANGEBYSCORE and HMGET,
decoded the whole queue, and the matcher then truncated to its candidate
limit *before* filtering by playlist. A large casual prefix could
therefore leave the ranked worker with zero candidates indefinitely even
while ranked tickets were queued further down the set.
Mutual erasure: each matcher captured only its own playlist as the
durable source, but Rebuild replaced the shared keys, so a casual repair
wiped ranked projections and vice versa.
Namespace the keys per playlist, push the limit into Redis (LIMIT 0 N)
so reads no longer scale with total queue depth, and scope Rebuild to
one namespace. Rebuild now rejects a candidate whose playlist does not
match the namespace, which would reintroduce the starvation. Upsert
derives the namespace from the candidate; Remove takes the playlist,
since a ticket ID alone no longer identifies its namespace.
Add tests for a 300-deep casual backlog not starving ranked, for neither
playlist's rebuild erasing the other, and for the limit being applied
without losing enqueue ordering.
Closes part of the 'live Redis failover' gap in §8.46, found by
reproducing a genuine Redis outage (not just an empty/partial cache)
against CandidateProjection.Snapshot with a killed miniredis instance.
CandidateProjection.Snapshot funnelled two different situations into
the same code path: the index erroring outright (Redis unreachable)
and the index coming back empty (ambiguous — a genuinely empty queue,
or a lost keyspace). Both went through Repair, which itself calls
Index.Rebuild — a second Redis round-trip that fails for exactly the
same reason the first one did. The result: a real Redis outage, or
the window during a failover, made Snapshot fail outright even though
PostgreSQL — the documented authoritative source everywhere
(RedisCandidateIndex's own comment, cmd/matcher, cmd/control-plane's
--redis-addr help text all call it a rebuildable/optional
acceleration layer) — was completely healthy. Matchmaking would stop
entirely on a Redis outage despite the architecture explicitly not
requiring that.
Snapshot now falls back to serving Source (PostgreSQL) directly
whenever the index errors OR comes back empty, and only best-effort
attempts to repopulate Redis afterward — that attempt's outcome is
deliberately ignored, since a caller must never be denied service
just because the opportunistic rebuild also hit the same down Redis.
Snapshot still fails when Source itself is unavailable; the fallback
is not unconditional.
Verified: reproduced the bug first (killed-miniredis Snapshot call
failed even though Source was healthy), then fixed it. go build/vet
clean; all pre-existing store-package tests pass unmodified,
including the two live-redis:7-alpine-container tests
(TestRealRedisCandidateIndexUpsertSnapshotRemove,
TestRealRedisCandidateProjectionRepairsAfterFlush, run against a real
container and torn down after). Two new tests cover the fallback
directly (killed miniredis, Source still served, exactly one Source
call) and that the fallback is not unconditional (both Redis and
Source down still fails). Full go test ./... -race clean across
every server package.
Remaining: live matcher-worker-under-load-during-failover integration,
i.e. running the actual matcher process against a real Redis that
goes down mid-run under concurrent load, not just this unit-level
reproduction.
Josh Creek