perf(sections): cut the fixed cost out of the home sections response

[CoffeeKnyte]

The home screen now returns in a fifth of the time it used to: production p50 fell from
1030ms to 195ms and the mean from 1074ms to 253ms, measured over 3,211 real requests in the
19.6 hours since deploy against 1,028 requests in the 8.3 hours before it. The change also fixes a
pre-existing bug that hid quality badges entirely from any profile with a library allow-list.

One commit: the fix plus the phase instrumentation that proves where the time went.

Related work

Third in the sections performance series, after #984 (stored parent IDs for episode totals) and
#947 (Continue Watching stops re-reading watch history). It branches directly off #947's merge
commit.

It does not fix anything those two broke, and it does not touch their code — the diff against
origin/main leaves internal/catalog/continue_watching_progress.go untouched. They removed
per-section costs; this removes the fixed cost every request paid regardless of section, which is
what was left once theirs landed. The badge bug below is older than all three: it dates to
c085b12f, the initial migration.

One thing #947 introduced is still open and this PR does not address it: the
continue-watching: superseded-episode walk hit page cap WARN fires at a comparable rate before
and after (23/h and 26/h), so whatever it indicates is unchanged.

Related issue: N/A — no issue or epic exists for the sections latency work; #947 and #984 are
pull requests. Worth opening one if this series continues.

Problem

The home screen took about a second for everyone, every time. Opening Silo on any client
meant waiting roughly a second before the first row of posters appeared. It was not a slow
network or a slow device — it was the server, and it was consistent: 96.6% of home-screen
requests took 900ms or more, and only 7 requests out of 1,028 came back in under 300ms. The
delay showed up identically on Android, on tvOS, and on iOS, so no client team could fix it on
their side.

The cost scaled with the size of the library, not with what was on screen. The home screen
shows about 30 rows of roughly 20 posters each. To draw the small quality badges on a poster
(4K, HDR, Atmos), the server was reading every media file behind every card — and for a TV
series card, that meant every episode file of the entire show. One series in this library has
8,302 files, all of them read to render a single badge. A row of 20 children's shows pulled
2,723 database rows and about 6 MB of data to draw 20 badges. All but 20 of those rows were
decoded and thrown away.

Households with restricted libraries saw no quality badges at all. Separately from the
speed problem, any profile limited to a subset of libraries — a kids' profile, a shared-account
guest — got posters with no 4K, HDR, or audio badges anywhere on the home screen. The badges
were not "sometimes wrong"; they were entirely absent for those profiles, and had been for as
long as the feature has existed. Nobody filed an issue for it, so it appears to have been read
as "this build just doesn't show badges" rather than as a bug.

There was no way to tell which part of the request was slow. The endpoint reported one
number — total duration — so every explanation for the second was a guess. Two plausible
guesses turned out to be wrong, and there was no evidence available to settle it either way.

Solution

perf(sections): cut the fixed cost out of the home sections response

Reduce each card to one file inside PostgreSQL. listOverlaySummaries
(internal/sections/fetcher.go:1207) now picks the single best file per card with
DISTINCT ON (group_key) (internal/sections/fetcher.go:1251) instead of returning every
candidate file and reducing in Go. Only the winner's wide columns — including the four JSON
track blobs — are fetched, via a join back on winners.id; the ranking sorts narrow
(group_key, id, rank) tuples first, because sorting the wide rows costs measurably more.

The ranking mirrors overlays.BestFile (internal/overlays/summary.go:60) exactly, down to
the final tiebreak content_id ASC, episode_id ASC, id ASC — the old Go path kept the first
file in the slice, and the slice arrived in that order. overlays.ResolutionRank and
overlays.RangeRank (internal/overlays/summary.go:66,70) were exported so a test can pin the
SQL against the Go implementation rather than against a second hand-written copy of the rules.

Measured against the production database: 580 mixed cards went from 4,578 rows / 357ms to
580 rows / 140ms; 300 series cards from 8,639 rows / 636ms to 300 rows / 150ms; the Kids Shows
row from 2,723 rows / ~372ms to 20 rows / 100ms.

Push the access predicate into SQL, and fix the bug that surfaced. The old query filtered
files in Go with catalog.FilterMediaFilesByAccess (old fetcher.go:1208), but its SELECT
list (old fetcher.go:1108) never included media_folder_id. Every MediaFile therefore
carried MediaFolderID == 0, and FileAllowedByAccess
(internal/catalog/access_filter.go:189) compares exactly that field against
filter.AllowedLibraryIDs. Folder 0 is in nobody's allow-list, so for any profile with a
non-nil allow-list every file was dropped, BuildSummary received an empty slice, and the
card got no summary at all.

The new path applies the same predicate as a SQL WHERE clause through
catalog.MediaFileAccessSQL (internal/catalog/access_filter.go:260), a new helper that
mirrors FileAllowedByAccess field for field — allow-list, disabled libraries, and the
quality ceiling. Because the filter is now applied against the real column instead of a
zero-valued struct field, restricted profiles get their badges. This is a user-visible change
in those households: badges appear where there were none.

Cache summaries per access scope. overlaySummaryCacheScope
(internal/sections/fetcher.go:1127) fingerprints only the parts of the access filter that can
change the answer, and summaries are cached under scope\x00contentID with a 5-minute TTL
(internal/sections/fetcher.go:1114). A card with no usable file caches as a nil summary
rather than as a miss, so it is not re-queried every request. In steady state the second and
later requests read zero rows.

Caching is only sound because of the behaviour change below.

Run the six enrichment lookups concurrently. buildSectionsResponse
(internal/api/handlers/sections.go:1315) issued six independent database round trips over
every card on the page — overlays, playable targets, user states, image URLs, episode meta,
manga chapter meta — one after another, and only combined them at the end. They now run
together under a sync.WaitGroup, so the phase costs the slowest lookup rather than their sum.
Fan-out stays at six, matching what FetchAll already takes, so peak pool usage per request is
unchanged — the two phases never overlap.

Add phase timing, and lower the aggregate alarm. sectionPhaseTimer
(internal/api/handlers/sections.go:603) records resolve / next_up / fetch_all / build_response / write and emits the whole breakdown as one line from HandleHomeSections
(internal/api/handlers/sections.go:635): WARN past 500ms
(slowHomeSectionsThreshold, internal/api/handlers/sections.go:598), DEBUG below, so the
phases are always available without making a slow request indistinguishable from a fast one.
slowAggregateFetchThreshold (internal/sections/fetcher.go:69) dropped from 1s to 500ms for
the same reason: a threshold set at the middle of the distribution almost never fires and
reports nothing.

This instrumentation is what turned the diagnosis from argument into measurement, and it is
what produced the phase table below.

Deliberate behaviour change

A series that shares a page with one of its own episodes now reports the best file in the
whole show. Previously the episode's file was removed from the series' candidate pool, so the
same series card showed different badges depending on which other cards happened to be on the
page with it. Page-dependent badges were the reason the result could not be cached; making the
answer page-independent is both more correct and what makes the cache sound. Verified against
production data across four card samples — the only differences are the 28 expected ones in the
series-plus-their-own-episodes sample.

Results

Production, GET /api/v1/home/sections, status 200. Before: the container running the previous
build, 2026-09-06T04:00Z until the deploy. After: the current container, deployed
2026-09-06T12:21:11Z, read at 2026-09-07T07:58Z. Request rate was comparable across both
windows (123/h before, 164/h after), so this is not a traffic artifact. All "after" figures come
from a single frozen log snapshot, because the live container keeps appending.

	n	min	p50	p90	p95	p99	max	mean
Before	1028	65	1030	1275	1499	2299	2863	1074
After	3211	45	195	388	506	1075	5437	253
Change		−31%	−81%	−70%	−66%	−53%	see below	−76%

The shape of the distribution changed, not just its percentiles. The old mode was a tall spike
in the 1000–1249ms bucket holding 54% of all requests; the new mode is the 0–249ms bucket
holding 74%.

duration	before	after
0–249ms	0.7%	73.5%
250–499ms	0.8%	21.4%
500–749ms	1.2%	3.1%
750–999ms	32.1%	0.9%
1000–1249ms	54.0%	0.3%
≥1250ms	11.2%	0.9%

Requests at or above 900ms fell from 993 of 1028 (96.6%) to 43 of 3211 (1.3%). Requests under
300ms rose from 7 (0.7%) to 2,639 (82.2%).

By client family

The win is not one platform. All three client families improved by roughly the same proportion.

client	before mean	after mean	before p50	after p50	n after
ktor (Android)	1082	252	1033	195	2826
SiloTV (tvOS)	977	186	986	164	195
Silo iOS	973	332	970	227	190

ktor-client is the Silo Android phone/TV client — it is the only non-Apple user agent that
reaches this endpoint at all. SiloTV covers tvOS including the Top Shelf extension, Silo is
iOS. No browser hit /api/v1/home/sections during either window, so the web UI is unmeasured
here; it runs the same server code, so it should see the same improvement, but that is inference
rather than a reading.

The iOS mean is inflated by three 5.2–5.4s outliers discussed below; excluding them it is
252ms (p50 224ms, p95 423ms, n=187), in line with the other two.

Phase breakdown

159 of 3,211 requests (5.0%) crossed the 500ms WARN threshold. Across those 159 lines:

phase	mean	p50	p90	max	share of total
resolve_ms	2	2	4	12	0.2%
next_up_ms	0	0	1	2	0.0%
fetch_all_ms	231	159	644	1175	25%
build_response_ms	679	525	861	5258	73%
write_ms	22	23	26	40	2.3%
total_ms	936	713	1552	5432

build_response exceeds fetch_all on 146 of the 159 slow requests and accounts for 73% of
their combined time. That settles the question the instrumentation was added to answer: the
remaining cost is the enrichment pass, not FetchAll. Two earlier hypotheses — that
FetchAll concurrency waves were the bottleneck, and that per-section costs measured on
/home/sections/{id}/items were section-fetch costs — are both disproven by this table and
should not be re-litigated. Typical pages carry 31 sections and ~550 items.

Jellyfin clients

jellycompat does not touch this code. ListOverlaySummaries has exactly three callers —
internal/api/handlers/sections.go:1364, internal/api/handlers/watch_tonight.go:355 and
internal/api/handlers/recommendations.go:655 — all on the v1 surface, and nothing under
internal/jellycompat/ references overlay summaries or buildSectionsResponse at all. Jellyfin
clients build their home screen from /Items/Latest, /Shows/NextUp and /UserItems/Resume,
which are a separate view over the catalog.

Measured anyway, to confirm nothing regressed. Per-route, status < 400, excluding streaming and
the 60s /socket long-poll:

route	before p50	after p50	before p95	after p95	after n
/Items/Latest	180	56	434	420	3588
/Users/{id}/Items/Latest	46	27	297	265	2687
/Items/{id}/Download	42	31	156	144	13286
/UserItems/Resume	110	106	433	437	1108
/Shows/NextUp	107	114	570	389	1148
/Shows/{id}/Episodes	42	42	74	83	5003
/Items	0	0	214	238	8117
/Sessions/Playing/Progress	5	5	9	9	37241

Nothing regressed. Several routes improved, most visibly /Items/Latest. I would not attribute
that to this change — the plausible mechanism is reduced connection-pool and buffer pressure now
that the sections endpoint no longer pulls millions of rows — but the traffic mix also differs
between the two windows, so treat it as "no regression, possibly a bonus" rather than a claim.

Risk / follow-ups

• Badges appear where they did not before. Any profile with a library allow-list will
  suddenly see 4K/HDR/audio badges on the home screen. This is the bug fix landing, not a
  regression, but it is a visible change for those households and worth saying out loud in
  release notes. No issue was ever filed for the missing badges (searched open and closed), so
  nobody is expecting the change.
• Badges can now be up to 5 minutes stale because of the summary cache. A file replaced
  with a better version will keep showing the old badge until the TTL expires. Acceptable for
  decorative badges; not acceptable if anything load-bearing is ever derived from them.
• The maximum got worse: three 5.2–5.4s requests, all from one user. 14:33, 17:21 and
  21:29, every one of them the same account on the same iOS build, fetch_all_ms ~130ms and
  build_response_ms 5,071–5,258ms. That user's other 16 requests in the window are normal
  (p50 379ms), and no other request on the server stalled at those moments, so it is neither a
  server-wide event nor a permanently slow profile. There is no context.WithTimeout anywhere
  in the enrichment path, so despite how consistent the ceiling looks it is not a code deadline
  — the most likely candidate is the image resolver's ladder fallback
  (internal/metadata/image_resolver.go:338) taking a cold-cache walk with real storage HEADs
  behind it. Not a regression this change introduced, and it predates the change in kind; it was
  simply invisible before, when every request cost a second anyway. Worth a follow-up issue, not
  a blocker.
• One cold-cache request per hour still costs ~1.5s. Requests at :45–:52 past most hours
  land at 1.4–1.7s with both fetch_all_ms (~650ms vs ~150ms typical) and build_response_ms
  (~800–950ms) elevated — a cache-expiry cliff paid by whoever arrives first. Steady-state
  performance is unaffected; a background refresh would remove it.
• Five enrichment stages are still individually unmeasured. build_response is now the
  dominant remaining cost but is timed as a whole. The named suspects inside it are
  catalog.PlayableTargetResolver.Resolve (serial progress batches of 500),
  resolveItemUserStatesWithOptions (six inner serial round trips that this change did not
  parallelise), and resolveSectionItemImageURLs (presigns up to ~1,740 paths).
• The structural question is untouched. The server still builds ~31 sections when the
  client shows three or four above the fold. That is the largest remaining win, and it is a v1
  API shape change needing silo-apple and silo-android coordination — a product decision,
  not a patch.
• Client-visible surface. No API shape change, so no client work is required. jellycompat
  does not use this path and needs no parity change. No docs/*-api.md update is needed.
• internal/catalog/access_filter.go gained MediaFileAccessSQL, which duplicates
  FileAllowedByAccess in SQL. The two must stay in step; they are pinned by test, but a
  future field added to one and not the other would diverge silently.

Verification

• gofmt -l internal/ clean; go build ./... and go vet clean on the touched packages.
• go test ./internal/sections/... ./internal/overlays/... ./internal/catalog/... ./internal/api/handlers/...
  green (re-run against the deployed commit).
• golangci-lint --new-from-merge-base=origin/main: 0 issues.
• TestOverlaySummaryRankSQLMatchesGo pins the SQL ranking against overlays.BestFile over a
  VALUES list. It caught four real divergences during development: jsonpath eating the
  backslash in \s; hasDolbyVision reading the raw video_range_type where
  hdrTypeFromTracks trims it; BTRIM stripping only spaces where strings.TrimSpace strips
  the whole ASCII set; and jsonpath treating JSON null as != "".
• TestOverlaySummariesIndependentOfPageAndCache pins page- and cache-independence against a
  temporary media_files fixture.
• Old vs new overlay output compared against production data across four card samples
  (mixed 580, series 300, episodes 400, series-plus-their-own-episodes 360): zero unexpected
  differences. The 28 differences in the last sample are the intended page-independence change.
• go test ./... green; go test -race green on the section handler tests. Two
  internal/playback failures on one full-suite run are pre-existing and environment-dependent:
  one is flaky under load, and TestResolveCopySeekAnchorMatchesRealLongGOPHEVC fails
  identically on a clean origin/main worktree because it shells out to ffmpeg.
• Deployed to production and measured against 19.6 hours of real traffic, 3,211 home-screen
  requests, from a single frozen log snapshot. Numbers above.
• No new error classes in the deploy window. The 8 loading overlay summaries ERRORs present
  in the before window — client cancellations during the long row iteration — are gone
  entirely. Zero panics. The plugin batch image resolution failed ERRORs are pre-existing
  (172 in the before window) and are context canceled from the tvdb image plugin during a
  jellycompat request surge; they do not touch this path, whose requests during the largest
  burst ran 193–282ms.
• Running image confirmed identical to the built silo:local
  (sha256:b410b937e34a6…), so the measured window is this code.

AI-use disclosure

Written with AI assistance: Claude Code (claude-opus-5) did the investigation, the
implementation, and the production before/after measurement. All numbers are from production
logs and the production database; the reasoning and conclusions were reviewed by the author.

Summary by CodeRabbit

• Performance

  • Improved loading speed for home sections by processing content more efficiently.
  • Added caching for overlay summaries to improve repeat access times, including empty results.
  • Reduced the threshold for identifying slow section loading.

• Access and Playback

  • Overlay summaries now respect library access permissions and playback-quality limits.
  • Improved selection of the best available media file for each content group.
  • Improved consistency when media resolutions contain surrounding whitespace.

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📒 Files selected for processing (3)

• internal/catalog/access_filter.go
• internal/sections/fetcher.go
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📝 Walkthrough

Walkthrough

Changes

The change adds access-aware SQL helpers, Unicode whitespace parity tests, cached overlay-summary queries, and concurrent home-section enrichment. Request timing now records phase durations, item counts, total duration, and slow requests at a 500 ms threshold.

Sections overlay performance

Layer / File(s)	Summary
Access SQL and ranking contracts internal/catalog/access_filter.go, internal/overlays/summary.go, internal/sections/overlay_summary_rank_sql_test.go	SQL helpers mirror access filtering and quality ceilings. Exported wrappers expose Go ranking logic. Tests compare SQL and Go results for Unicode-whitespace-padded resolutions.
Cached overlay summary query internal/sections/fetcher.go, internal/sections/overlay_summary_cache_test.go, internal/sections/overlay_summary_grouping_sql_test.go	Overlay summaries use five-minute caches scoped by access filters. The grouped query selects accessible files with deterministic ranking, caches empty results, and reports query and scan errors. Tests cover cache scopes, pagination independence, and cache warming.
Concurrent section enrichment internal/api/handlers/sections.go, internal/sections/fetcher.go	Home section handling runs independent enrichment operations concurrently and waits before response assembly. Timing logs include phase durations, item counts, total duration, and the 500 ms slow-request threshold.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: 🔵 Low · up to e08aa

The endpoint now caches access-scoped overlay summaries for five minutes, improving response time, but Fetcher lifecycles may retain cache janitor goroutines. This is a low merge-readiness risk that should be addressed or tracked by the owner.

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant HandleHomeSections
  participant Fetcher
  participant PostgreSQL
  Client->>HandleHomeSections: Request home sections
  HandleHomeSections->>Fetcher: Start concurrent enrichment
  Fetcher->>PostgreSQL: Query uncached accessible files
  PostgreSQL-->>Fetcher: Return ranked files
  Fetcher-->>HandleHomeSections: Return summaries and enrichment data
  HandleHomeSections-->>Client: Write assembled response and timing logs

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❌ Failed checks (1 warning)

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Title check	✅ Passed	The title clearly describes the main change: reducing the fixed performance cost of the home sections response. It is specific and concise.
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Actionable comments posted: 1

🧹 Nitpick comments (1)

internal/sections/fetcher.go (1)

102-104: 🩺 Stability & Availability | 🔵 Trivial | 💤 Low value

Close test-created Fetcher instances.

cache.NewTTLCache starts one sweeper goroutine per initialized cache. overlay_summary_grouping_sql_test.go creates multiple Fetcher instances without closing them, so their sweepers remain until the test process exits. Add Fetcher.Close() and register cleanup for each test-created instance. Production Fetcher instances are fixed, process-lifetime owners, so this is not an unbounded production leak.

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In `@internal/sections/fetcher.go` around lines 102 - 104, Add a Close method to
Fetcher that releases its initialized overlaySummaryCache and register t.Cleanup
to call Close for every Fetcher created by overlay_summary_grouping_sql_test.go.
Ensure cleanup safely handles caches that were never initialized, while leaving
production Fetcher lifecycle behavior unchanged.

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Inline comments:
In `@internal/catalog/access_filter.go`:
- Around line 247-249: Update the quality-ceiling predicate generated by the
resolution-ranking logic to normalize Unicode whitespace consistently with Go
before applying UPPER and rank comparisons. Preserve the existing resolution
ranks and maxRank boundary behavior, and add a parity test covering a resolution
surrounded by Unicode whitespace.

---

Nitpick comments:
In `@internal/sections/fetcher.go`:
- Around line 102-104: Add a Close method to Fetcher that releases its
initialized overlaySummaryCache and register t.Cleanup to call Close for every
Fetcher created by overlay_summary_grouping_sql_test.go. Ensure cleanup safely
handles caches that were never initialized, while leaving production Fetcher
lifecycle behavior unchanged.

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• internal/api/handlers/sections.go
• internal/catalog/access_filter.go
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• internal/sections/overlay_summary_grouping_sql_test.go
• internal/sections/overlay_summary_rank_sql_test.go

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