From ec37e237185e46953e586e4bd38341477dfe271d Mon Sep 17 00:00:00 2001
From: Deluan <deluan@navidrome.org>
Date: Fri, 4 Sep 2026 22:36:13 -0400
Subject: [PATCH] perf(pglite): purge unused tags with NOT EXISTS instead of
 NOT IN

On a 97k-track library the tag purge in the scanner GC ran for many
minutes: PostgreSQL re-evaluates a NOT IN subquery of ~1M tag references
per tag row. A materialized set with NOT EXISTS takes 1.4 s locally
versus 55 s for NOT IN at that scale; work_mem made no difference.
---
 persistence/tag_repository.go | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/persistence/tag_repository.go b/persistence/tag_repository.go
index 67c4aa4d9..dec9434d8 100644
--- a/persistence/tag_repository.go
+++ b/persistence/tag_repository.go
@@ -82,16 +82,20 @@ func (r *tagRepository) GetAll(name model.TagName, options ...model.QueryOptions
 }
 
 func (r *tagRepository) purgeUnused() error {
+	// NOT EXISTS over a materialized set: NOT IN re-scans the ~1M-row subquery per tag (40x slower).
 	del := Delete(r.tableName).Where(`
-	id not in (select elem->>'id'
-	from album
-	cross join lateral jsonb_each(coalesce(album.tags, '{}'::jsonb)) as e(k, arr)
-	cross join lateral jsonb_array_elements(e.arr) as elem
-	UNION
-	select elem->>'id'
-	from media_file
-	cross join lateral jsonb_each(coalesce(media_file.tags, '{}'::jsonb)) as e(k, arr)
-	cross join lateral jsonb_array_elements(e.arr) as elem)
+	not exists (
+	  with used(id) as materialized (
+	    select elem->>'id'
+	    from album
+	    cross join lateral jsonb_each(coalesce(album.tags, '{}'::jsonb)) as e(k, arr)
+	    cross join lateral jsonb_array_elements(e.arr) as elem
+	    union
+	    select elem->>'id'
+	    from media_file
+	    cross join lateral jsonb_each(coalesce(media_file.tags, '{}'::jsonb)) as e(k, arr)
+	    cross join lateral jsonb_array_elements(e.arr) as elem)
+	  select 1 from used where used.id = ` + r.tableName + `.id)
 `)
 	c, err := r.executeSQL(del)
 	if err != nil {