fix(explore): let a slow archive node finish, and read the 404 back

Explore's album art was almost entirely missing: 5 of 24 cards on the shelves had a cover, and those five were the ones already on disk. The Cover Art Archive answers `front-250` with a 307 to an Internet Archive storage node, and those nodes are slow. Measured against the twelve albums on Explore's own shelves, a successful fetch took 14-16 s and a failing one 13-17 s, against a client timeout of 10. So every live fetch died, and a timeout writes nothing and says nothing -- which is why this reads as "Explore has no album art" rather than as a slow upstream. The timeout is 30 s, chosen to clear the measured range: the fetch is off the critical path, so waiting costs nothing and giving up early costs the whole page. Two things beside it, both found on the way. `writeCache(mbid, nil)` has recorded "the archive has no art for this" as an empty file since it was written, and nothing has ever read it back: `readCache` returns "" for an empty file, which is indistinguishable from a miss. So every art-less release group was re-fetched from CAA on every render that asked about it. A third of the shelves are art-less, so that was a third of the page spending a live request to be told again what the last one said. `knownMissing` reads it, on both the release-group and the release path. And the frontend marked a failed fetch as permanently answered for the session, so a timed-out cover never retried within it. It drops the marker instead; a genuine 404 is now answered from disk, so re-asking one costs nothing. Measured after: 23 of 24. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MeQt5hgXg5YGoNZQ9ozG7L
2026-08-17 22:09:14 -04:00
parent 0019310ca4
commit 40984f6086
2 changed files with 65 additions and 6 deletions
@@ -1509,9 +1509,24 @@ export class ExploreView extends ViewLifecycleMixin(LitElement) implements Conte
                            if (url) {
                                this.thumbnailCache.set(req.mbid, url);
                                this.requestUpdate();
+
+                                return;
                            }
+
+                            // An empty answer is not necessarily "there
+                            // is no art" — a slow Internet Archive node
+                            // is answered by a timeout, which looks
+                            // exactly the same from here. Drop the
+                            // in-flight marker so the next time this
+                            // release group is on screen it is asked
+                            // again; the backend records a genuine 404
+                            // on disk and answers that one instantly,
+                            // so a real miss costs nothing to re-ask.
+                            this.thumbnailCache.delete(req.mbid);
                        })
-                        .catch(() => {});
+                        .catch(() => {
+                            this.thumbnailCache.delete(req.mbid);
+                        });
                }
            })
            .catch(() => {