Claudio Ortolina
74 lines
2.6 KiB
Markdown
74 lines
2.6 KiB
Markdown
---
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id: ML-169.8
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title: "Fix: StatsLive.Index 10 sync queries blocking TTFB"
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status: To Do
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assignee: []
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created_date: "2026-05-19 11:48"
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labels:
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- perf
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- fix
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dependencies: []
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references:
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- >-
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backlog/documents/doc-27 -
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Phase-4-Performance-Audit-Low-Hanging-Fruit-Findings.md
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modified_files:
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- lib/music_library_web/live/stats_live/index.ex
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parent_task_id: ML-169
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priority: high
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ordinal: 29000
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---
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## Description
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<!-- SECTION:DESCRIPTION:BEGIN -->
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Fix performance issue where the StatsLive.Index mount callback executes 10 synchronous Ecto queries before returning, blocking the initial render (TTFB) on the home page.
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## Problem
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The mount callback executes 10 synchronous queries before returning `{:ok, socket}`:
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1. `Collection.get_latest_record()` — ORDER BY purchased_at LIMIT 1
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2. `Collection.count_records_by_artist(limit: 20)` — json_each + GROUP BY
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3. `Collection.count_records_by_genre(limit: 20)` — json_each + GROUP BY + subquery exclusion
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4. `Collection.count_records_by_release_year(limit: 20)` — substr + GROUP BY
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5. `Collection.get_records_on_this_day(date)` — strftime + ORDER BY
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6. `Collection.count_records_by_format()` — GROUP BY format
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7. `Collection.count_records_by_type()` — GROUP BY type
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8. `Wishlist.count()` — FTS search count
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9. `ListeningStats.recent_activity(timezone)` — 4 correlated subqueries × 100 rows
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10. `ListeningStats.scrobble_count()` — simple COUNT
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## Impact
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10 blocking queries on the home page is the worst TTFB bottleneck in the app. The `assign_async` pattern is already in use for TopAlbums/TopArtists on the same page — apply it consistently.
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## Files
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- `lib/music_library_web/live/stats_live/index.ex:67-109` — mount callback
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## Fix
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Use `assign_async` to defer non-critical queries. The simple ones (collection_count, wishlist_count, scrobble_count for the counter badges) can stay synchronous since they're fast. Move the heavy ones to `assign_async`:
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- `count_records_by_artist` / `count_records_by_genre` / `count_records_by_release_year`
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- `get_records_on_this_day`
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- `recent_activity` (the most expensive — 4 correlated subqueries)
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- `get_latest_record`
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Show skeleton/loading placeholders while async data loads.
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<!-- SECTION:DESCRIPTION:END -->
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## Acceptance Criteria
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<!-- AC:BEGIN -->
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- [ ] #1 StatsLive.Index mount completes in under 200ms (sync queries only)
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- [ ] #2 Charts and activity feed load with loading skeleton placeholders
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- [ ] #3 Counter badges (collection, wishlist, scrobbles) show immediately
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- [ ] #4 No visual flash of empty data containers
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- [ ] #5 Assigns that are now async handle nil/failure states gracefully
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<!-- AC:END -->
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