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perf(db): the channel manager and the feed sidebar read an index, not the video heap

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GET /api/channels summed every subscribed channel's videos by reading each video's heap page
(681 MB on prod): 51-61 ms warm, but 2.25 s on a first open and 6.4 s under EXPLAIN once the
table had left memory. /feed/summary and /feed/years did the same (~140 ms warm, ~800 ms cold).
Migration 0095 replaces ix_videos_channel_pub_desc with the same key INCLUDING the columns
those queries read, so they are Index Only Scans over a 25 MB index. A test holds the queries
and the index's column list together.

The admin Configuration page did a db.get per setting (two for an unset one): it now reads
every override in one query (~40 ms of ~55 on prod).
This commit is contained in:
peter
2026-10-02 03:16:37 +02:00
parent 20010178b0
commit e995c664c6
7 changed files with 220 additions and 26 deletions
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backend/app/models.py
+6 -4
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@@ -330,10 +330,12 @@ class Video(Base, TimestampMixin):
__tablename__ = "videos"
id: Mapped[str] = mapped_column(String(16), primary_key=True) # video id
# No standalone channel_id index: the composite `ix_videos_channel_pub_desc`
# (channel_id, published_at DESC NULLS LAST, id) from migration 0067 leads with channel_id, so it
# serves every channel_id lookup (FK cascade, sync upsert, channel-detail) AND the per-channel feed
# sort. Like the search_vector GIN, this composite is migration-defined, not an inline `index=True`.
# No standalone channel_id index: the composite `ix_videos_channel_pub_cover`
# (channel_id, published_at DESC NULLS LAST, id) from migration 0095 leads with channel_id, so it
# serves every channel_id lookup (FK cascade, sync upsert, channel-detail) and the per-channel feed
# sort. Its INCLUDEd columns make the channel manager's sums and the feed sidebar's counts Index Only
# Scans (no heap): a column those queries start reading belongs in it (test_channel_list_index_only).
# Like the search_vector GIN, this composite is migration-defined, not an inline `index=True`.
channel_id: Mapped[str] = mapped_column(ForeignKey("channels.id", ondelete="CASCADE"))
title: Mapped[str | None] = mapped_column(Text) # normalized for display (see app.titles)
original_title: Mapped[str | None] = mapped_column(Text) # raw YouTube title, preserved