perf: denormalize content-warning filter to manga_content_warnings

The content-warning include/exclude filter (and its count) ran a correlated
page_content_warnings->pages->chapters join per candidate manga — O(mangas *
pages) on every filtered list. Add a manga_content_warnings(manga_id, warning)
table holding each manga's deduped warning union, maintained by triggers that
recompute an affected manga's set (delete+reinsert of the tiny five-label set,
robust across page/chapter/manga cascade deletes), backfilled in the migration.
The filter is now a single indexed lookup.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/Cargo.lock

@@ -1558,7 +1558,7 @@ checksum = "c41e0c4fef86961ac6d6f8a82609f55f31b05e4fce149ac5710e439df7619ba4"
 
 [[package]]
 name = "mangalord"
-version = "0.124.22"
+version = "0.124.23"
 dependencies = [
  "anyhow",
  "argon2",

backend/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.124.22"
+version = "0.124.23"
 edition = "2021"
 default-run = "mangalord"
 

backend/migrations/0036_manga_content_warnings.sql

@@ -0,0 +1,103 @@
+-- Denormalized manga -> content-warning set.
+--
+-- The list filter previously tested each candidate manga with a correlated
+-- `page_content_warnings -> pages -> chapters` join, i.e. O(mangas * pages) on
+-- every filtered list AND its count. This table holds the DISTINCT union of a
+-- manga's page warnings so the filter is a single indexed lookup.
+--
+-- Kept in sync by triggers that recompute an affected manga's set from current
+-- data (the set is tiny — at most the five moderation labels — so a
+-- delete-and-reinsert per change is cheap and always correct, sidestepping the
+-- cascade-ordering hazards of incremental maintenance).
+
+CREATE TABLE manga_content_warnings (
+    manga_id uuid NOT NULL REFERENCES mangas(id) ON DELETE CASCADE,
+    warning  text NOT NULL
+                CHECK (warning IN ('sexual', 'nudity', 'gore', 'violence', 'disturbing')),
+    PRIMARY KEY (manga_id, warning)
+);
+
+-- warning -> mangas, for the include/exclude list filters.
+CREATE INDEX manga_content_warnings_warning_idx ON manga_content_warnings (warning);
+
+-- Recompute a single manga's warning set from the live per-page rows.
+CREATE OR REPLACE FUNCTION mcw_refresh_for_manga(mid uuid) RETURNS void AS $$
+BEGIN
+    -- Skip when the manga is gone (e.g. mid-cascade of a manga delete) so we
+    -- never re-insert a row that would violate the FK / resurrect a deleted set.
+    IF NOT EXISTS (SELECT 1 FROM mangas WHERE id = mid) THEN
+        RETURN;
+    END IF;
+    DELETE FROM manga_content_warnings WHERE manga_id = mid;
+    INSERT INTO manga_content_warnings (manga_id, warning)
+    SELECT DISTINCT mid, pw.warning
+      FROM page_content_warnings pw
+      JOIN pages p    ON p.id = pw.page_id
+      JOIN chapters c ON c.id = p.chapter_id
+     WHERE c.manga_id = mid;
+END;
+$$ LANGUAGE plpgsql;
+
+-- page_content_warnings changed for a page: refresh that page's manga.
+CREATE OR REPLACE FUNCTION mcw_on_pcw_change() RETURNS trigger AS $$
+DECLARE
+    mid uuid;
+    pid uuid := COALESCE(NEW.page_id, OLD.page_id);
+BEGIN
+    -- The page (and thus chapter) may already be gone when this fires as part
+    -- of a pages/chapters cascade; in that case the pages/chapters triggers do
+    -- the refresh instead, so a missing join here is harmless.
+    SELECT c.manga_id INTO mid
+      FROM pages p JOIN chapters c ON c.id = p.chapter_id
+     WHERE p.id = pid;
+    IF mid IS NOT NULL THEN
+        PERFORM mcw_refresh_for_manga(mid);
+    END IF;
+    RETURN NULL;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER mcw_pcw_ins AFTER INSERT ON page_content_warnings
+    FOR EACH ROW EXECUTE FUNCTION mcw_on_pcw_change();
+CREATE TRIGGER mcw_pcw_del AFTER DELETE ON page_content_warnings
+    FOR EACH ROW EXECUTE FUNCTION mcw_on_pcw_change();
+
+-- A page was deleted (directly, or via a chapter cascade): its
+-- page_content_warnings rows are already cascade-gone, so recompute from the
+-- chapter's manga. If the chapter is gone too, the chapters trigger covers it.
+CREATE OR REPLACE FUNCTION mcw_on_page_delete() RETURNS trigger AS $$
+DECLARE
+    mid uuid;
+BEGIN
+    SELECT c.manga_id INTO mid FROM chapters c WHERE c.id = OLD.chapter_id;
+    IF mid IS NOT NULL THEN
+        PERFORM mcw_refresh_for_manga(mid);
+    END IF;
+    RETURN NULL;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER mcw_page_del AFTER DELETE ON pages
+    FOR EACH ROW EXECUTE FUNCTION mcw_on_page_delete();
+
+-- A chapter was deleted (directly, or via a manga cascade): recompute from the
+-- chapter's manga. `chapters.manga_id` is on the row, so it is always available
+-- even after the child pages have cascaded; the refresh no-ops when the manga
+-- itself is being deleted.
+CREATE OR REPLACE FUNCTION mcw_on_chapter_delete() RETURNS trigger AS $$
+BEGIN
+    PERFORM mcw_refresh_for_manga(OLD.manga_id);
+    RETURN NULL;
+END;
+$$ LANGUAGE plpgsql;
+
+CREATE TRIGGER mcw_chapter_del AFTER DELETE ON chapters
+    FOR EACH ROW EXECUTE FUNCTION mcw_on_chapter_delete();
+
+-- Backfill from existing per-page rows.
+INSERT INTO manga_content_warnings (manga_id, warning)
+SELECT DISTINCT c.manga_id, pw.warning
+  FROM page_content_warnings pw
+  JOIN pages p    ON p.id = pw.page_id
+  JOIN chapters c ON c.id = p.chapter_id
+ON CONFLICT DO NOTHING;

backend/src/repo/manga.rs

@@ -144,17 +144,13 @@ const FILTER_WHERE: &str = r#"
     AND NOT EXISTS (
         SELECT 1 FROM unnest($6::text[]) AS req(w)
          WHERE NOT EXISTS (
-                SELECT 1 FROM page_content_warnings pw
+                SELECT 1 FROM manga_content_warnings mcw
-                  JOIN pages p    ON p.id = pw.page_id
+                 WHERE mcw.manga_id = mangas.id AND mcw.warning = req.w
-                  JOIN chapters c ON c.id = p.chapter_id
-                 WHERE c.manga_id = mangas.id AND pw.warning = req.w
              )
     )
     AND NOT EXISTS (
-        SELECT 1 FROM page_content_warnings pw
+        SELECT 1 FROM manga_content_warnings mcw
-          JOIN pages p    ON p.id = pw.page_id
+         WHERE mcw.manga_id = mangas.id AND mcw.warning = ANY($7::text[])
-          JOIN chapters c ON c.id = p.chapter_id
-         WHERE c.manga_id = mangas.id AND pw.warning = ANY($7::text[])
     )
 "#;
 

backend/tests/api_manga_warnings.rs

@@ -127,6 +127,46 @@ async fn list_filters_by_content_warning(pool: PgPool) {
     assert_eq!(ids, want);
 }
 
+#[sqlx::test(migrations = "./migrations")]
+async fn denormalized_warnings_track_chapter_deletion(pool: PgPool) {
+    // The denormalized manga_content_warnings table must stay in sync when the
+    // underlying pages disappear. Deleting the only chapter (which cascade-
+    // deletes its pages and their page_content_warnings) must drop the manga
+    // from the include filter.
+    let h = common::harness(pool.clone());
+    let gory = seed_manga(&pool, "Gory", &[&["gore"]]).await;
+
+    // Present in the denorm table and matched by the filter.
+    let count: i64 =
+        sqlx::query_scalar("SELECT count(*) FROM manga_content_warnings WHERE manga_id = $1")
+            .bind(gory)
+            .fetch_one(&pool)
+            .await
+            .unwrap();
+    assert_eq!(count, 1, "warning denormalized on insert");
+    assert_eq!(list_ids(&h.app, "cw_include=gore").await, vec![gory.to_string()]);
+
+    // Delete the chapter → cascade removes pages + page_content_warnings →
+    // trigger recomputes the (now empty) set for this manga.
+    sqlx::query("DELETE FROM chapters WHERE manga_id = $1")
+        .bind(gory)
+        .execute(&pool)
+        .await
+        .unwrap();
+
+    let count: i64 =
+        sqlx::query_scalar("SELECT count(*) FROM manga_content_warnings WHERE manga_id = $1")
+            .bind(gory)
+            .fetch_one(&pool)
+            .await
+            .unwrap();
+    assert_eq!(count, 0, "warning removed after chapter (and pages) deleted");
+    assert!(
+        list_ids(&h.app, "cw_include=gore").await.is_empty(),
+        "manga no longer matches the include filter"
+    );
+}
+
 #[sqlx::test(migrations = "./migrations")]
 async fn list_rejects_unknown_warning(pool: PgPool) {
     let h = common::harness(pool.clone());

frontend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.124.22",
+  "version": "0.124.23",
   "private": true,
   "type": "module",
   "scripts": {