A first backfill enqueues artists before albums at a single priority, so
the drain took them in that order. Artists resolve through a
rate-limited agent, and gate() waits for its permit while holding a
worker slot, so the whole pool sat asleep in the limiter with every
album queued behind it.
Measured on a 96k-track library (29,115 artists to 6,949 albums, 4:1):
zero albums resolved in seven minutes, and roughly 3.3 hours before the
first album cover would have appeared. Splitting the drain gives each
class its own slots: albums now finish in under eight minutes while
artists trickle at the same 2/s they were always limited to.
The two budgets are carved out of MaxOpenConns so a second pool cannot
take connections the scanner and the UI need. Dequeue filters by kind,
and the drain index leads with item_kind so each pool seeks to its own
work instead of scanning past the other's backlog.
Two gaps in when the pipeline re-resolves artwork:
The recheck job only requeued absent-state rows (hash=''), so an entity that was
never processed — added between scans, or on a server with the scanner disabled —
had no periodic safety net and stayed without artwork indefinitely. Add
EnqueueMissing(kind): a SQL set-difference enqueueing entities with no
item_artwork row at Recheck priority (ON CONFLICT DO NOTHING, so it never
disturbs a queued row). Run it once at startup and hourly alongside the
stale-absent recheck. Rename staleAbsentKinds -> recheckKinds accordingly.
Conversely, the config fingerprint included consts.Version, which embeds the git
SHA and so changed on every build, re-enqueueing every entity in the library
(~34k here) and re-querying external agents at the configured RPS for anything
without local art. Replace it with an explicit artworkEpoch constant, bumped
deliberately when resolution semantics change. The cases that motivated the
version input — absent art becoming available — are already covered by the
stale-absent and missing-row rechecks; only a corrected wrong-pick needs the
epoch. A test guards against reintroducing the version.
Entity-level artwork queries now take a typed model.Kind instead of a bare
prefix string. GetItemArtwork, DeleteForItem(s), GetInfoForItems,
EnqueueStaleAbsent, hydrateItemImages, enqueueBackfillKind and artwork.Refresh
convert to the prefix string only at the two real boundaries: the SQL
item_kind column (kind.Prefix() inside each repo) and external string inputs
(a new model.ParseKind for the nativeapi URL param, which also validates it).
The Backfill/stale-absent kind slices, the resolve.go dispatch switch, and the
kind→resource / kind→table lookup maps now use the Kind vars directly. The
queue lifecycle methods (MarkFailed/Delete*) keep string kinds — they operate
on a dequeued item's raw ItemKind column, which stays a string field, always
populated via kind.Prefix().
Removes every bare "al"/"ar"/… prefix literal from non-test code (27 -> 0);
behavior is unchanged.
Two serving-correctness fixes from review:
- serveMediaFile served a persisted mf embedded image even after EnableMediaFileCoverArt
was turned off (the setting isn't in the config fingerprint, so found rows aren't
reprocessed). Direct mf- URLs now honor the setting at serve time and fall back to
disc/album art.
- The file-backed staleness check compared whole-second mtimes, so a same-second content
replacement (two writes in one second, or timestamp-preserving tools) could serve
different bytes under the old hash + immutable policy. RefMtime is now unix-nanoseconds
(no schema change; int64 column), detecting sub-second changes where the filesystem
records them.
The provisional read-through and dangling re-enqueue used Enqueue, whose upsert
resets retry_at, so any browse of an unresolved entity that was backing off after
an external failure made it immediately eligible again — defeating the exponential
backoff during a provider outage. Add EnqueueBump, which raises priority but leaves
an existing row's retry_at intact, and route the serving path through it. Scan and
manual re-resolve keep Enqueue's reset (a detected change wants immediate retry).
Queue rows for deleted entities failed forever (Get -> ErrNotFound -> failed -> capped retries, unbounded). Add ArtworkQueueRepository.PurgeDangling, called from Prune next to the item_artwork purge. Separately, the found/absent path unconditionally deleted the dequeued row, erasing a concurrent scan re-enqueue; switch to DeleteIfUnchanged, which deletes only while retry_at still matches the dequeued value (verified retry_at is the column an Enqueue upsert resets).
Write falls through to a real write when the liveness touch fails, and sweep retention now matches the recorded mime's extension so obsolete variants are reclaimed.
