Index duplicate entries so moving their chapters doesn't take hours

CHANGELOG.md

@@ -43,6 +43,7 @@ The format is a modified version of [Keep a Changelog](https://keepachangelog.co
 - Fixed library entries without a date added getting their last update time as date added when updating from v0.20.x ([@AntsyLich](https://github.com/AntsyLich))
 - Fixed the app closing when WebView's page process crashed ([@AntsyLich](https://github.com/AntsyLich))
 - Fixed installing or updating an extension sometimes cancelling the install of another one ([@AntsyLich](https://github.com/AntsyLich))
+- Fixed updating from v0.20.x taking up to hours on libraries with many duplicate entries ([@AntsyLich](https://github.com/AntsyLich))
 
 ## [v0.21.0] - 2026-10-12
 ### Added

data/src/main/sqldelight/tachiyomi/migrations/17.sqm

@@ -31,6 +31,9 @@ WHERE (source, url) IN (
     HAVING count(*) > 1
 );
 
+-- Moving the chapters looks each one's entry up here, which without an index scans the whole table per chapter
+CREATE INDEX duplicate_mangas_id_index ON duplicate_mangas(_id);
+
 UPDATE mangas
 SET favorite_at = merged.favorite_at,
     initialized = merged.initialized,