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

id, title, status, assignee, created_date, updated_date, labels, dependencies, references, parent_task_id, priority

id	title	status	assignee	created_date	updated_date	labels	dependencies	references	parent_task_id	priority
ML-169.2	Phase 4: Performance low-hanging fruit audit	Done		2026-05-08 08:59	2026-05-19 07:44	audit ready		lib/music_library_web/live/stats_live/index.ex 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	ML-169	medium

Description

Identify unnecessary DB queries, redundant full-stream reloads, server round trips that could be client-side, missing optimistic UI opportunities, and blocking mount work that could be deferred.

Use QueryReporter skill to capture SQL traces for key page loads as evidence.

Key pre-flagged areas:

• StatsLive.Index: 5 synchronous queries in mount (TTFB impact)
• Display toggle (grid/list): full FTS query when CSS-only suffices
• ScrobbleRulesLive + OnlineStoreTemplateLive: redundant stream_insert + immediate full reload
• ScrobbledTracksLive + StatsLive: full stream reset on every scrobble batch instead of incremental insert
• Search inputs: verify phx-debounce is set

Acceptance Criteria

• #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

Final Summary

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.