ML-169.2: performed performance audit

backlog/tasks/ml-169.2 - Phase-4-Performance-low-hanging-fruit-audit.md

@@ -1,10 +1,10 @@
 ---
 id: ML-169.2
 title: "Phase 4: Performance low-hanging fruit audit"
-status: To Do
+status: Done
 assignee: []
 created_date: "2026-05-08 08:59"
-updated_date: "2026-05-11 06:46"
+updated_date: "2026-05-19 07:44"
 labels:
   - audit
   - ready
@@ -14,6 +14,10 @@ references:
   - lib/music_library_web/live_helpers/index_actions.ex
   - lib/music_library_web/live_helpers/record_actions.ex
   - .agents/skills/query-reporter/SKILL.md
+  - /tmp/queries-ml-audit.sql
+  - >-
+    backlog/documents/doc-27 -
+    Phase-4-Performance-Audit-Low-Hanging-Fruit-Findings.md
 parent_task_id: ML-169
 priority: medium
 ---
@@ -39,12 +43,36 @@ Key pre-flagged areas:
 
 <!-- AC:BEGIN -->
 
-- [ ] #1 SQL traces captured via QueryReporter for /collection, /collection/:id, /stats, /artists/:id
-- [ ] #2 Stream reset audit complete: every stream(:name, data, reset: true) call site evaluated for incremental-update alternatives
-- [ ] #3 Display toggle (grid/list) evaluated: confirmed whether CSS-only toggle can replace full DB reload
-- [ ] #4 StatsLive.Index mount blocking work quantified: 5 queries identified, assign_async feasibility assessed
-- [ ] #5 Search input debounce verified: phx-debounce attribute presence checked on all search forms
-- [ ] #6 Optimistic UI opportunities identified for delete, form save, toggle operations
-- [ ] #7 N+1 audit complete: handle_params, stream rendering, and LiveComponent Repo calls checked
-- [ ] #8 Findings report written as a Backlog.md document with file:line references, severity ratings, and fix recommendations
+- [x] #1 SQL traces captured via QueryReporter for /collection, /collection/:id, /stats, /artists/:id
+- [x] #2 Stream reset audit complete: every stream(:name, data, reset: true) call site evaluated for incremental-update alternatives
+- [x] #3 Display toggle (grid/list) evaluated: confirmed whether CSS-only toggle can replace full DB reload
+- [x] #4 StatsLive.Index mount blocking work quantified: 5 queries identified, assign_async feasibility assessed
+- [x] #5 Search input debounce verified: phx-debounce attribute presence checked on all search forms
+- [x] #6 Optimistic UI opportunities identified for delete, form save, toggle operations
+- [x] #7 N+1 audit complete: handle_params, stream rendering, and LiveComponent Repo calls checked
+- [x] #8 Findings report written as a Backlog.md document with file:line references, severity ratings, and fix recommendations
 <!-- AC:END -->
+
+## Final Summary
+
+<!-- SECTION:FINAL_SUMMARY:BEGIN -->
+
+## Audit Complete: 9 findings across 4 severity levels
+
+**SQL traces captured** via QueryReporter at `/tmp/queries-ml-audit.sql` for all 4 key pages (StatsLive, CollectionLive.Index, CollectionLive.Show, ArtistLive.Show).
+
+### Key findings:
+
+**HIGH severity (3)**:
+
+1. **Display toggle triggers full DB reload** — grid/list toggle in `handle_set_display` re-executes FTS search when CSS-only toggle suffices. Fix: remove `load_and_assign_records` call.
+2. **StatsLive.Index mount: 10 sync queries** — home page TTFB blocked by 10 sequential queries. `assign_async` already used elsewhere on the same page — extend it to cover heavy queries.
+3. **Scrobble updates trigger full stream reset** — every 5-minute cron batch causes `reset: true` on all connected clients for both StatsLive and ScrobbledTracksLive.
+
+**MEDIUM severity (4)**: 4. **Redundant stream_insert + immediate full reload** in ScrobbleRulesLive and OnlineStoreTemplateLive — `stream_insert` is immediately nullified by `load_and_assign_*`. 5. **Full resets on pagination** — `reset: true` on page changes when append could suffice. 6. **Missing optimistic UI** for delete operations — DB waits block UI. 7. **Correlated subqueries** in `ListeningStats.tracks_with_record_info_query` — 3 subqueries per row × 100 tracks.
+
+**PASS (2)**: 8. All search inputs have `phx-debounce` set. 9. No direct N+1 issues found in LiveView/LiveComponent layer (no direct Repo calls).
+
+Full report: `docs/backlog/documents/doc-27` — includes file:line references, SQL traces, and fix recommendations for each finding.
+
+<!-- SECTION:FINAL_SUMMARY:END -->