From c091ffdc6b2d8d4dd6f439d056c561bae7bd9a18 Mon Sep 17 00:00:00 2001
From: brandon <brandon@clinger.dev>
Date: Fri, 7 Aug 2026 22:51:45 -0400
Subject: Batch alternate version detection in DtoService to remove
 MediaSourceCount N+1

Browsing a page of videos with the MediaSourceCount field ran one alternate
version query per item, each opening a fresh DbContext. On a large library that
turned a single page into hundreds of sequential round trips and made the Items
endpoint take tens of seconds while holding a request thread the whole time.

Detect which videos own alternate versions once per page with a single query,
mirroring the existing people batch. Videos absent from that set have a single
media source, so the per item lookups are skipped for the common case. Behavior
is unchanged: a video with no alternates already resolved to a count of one.

Adds a regression test asserting the count resolves from the batch and the per
item lookups are never called.
---
 .../Item/LinkedChildrenService.cs                   | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

(limited to 'Jellyfin.Server.Implementations')

diff --git a/Jellyfin.Server.Implementations/Item/LinkedChildrenService.cs b/Jellyfin.Server.Implementations/Item/LinkedChildrenService.cs
index 5f1d9bf87a..2452f8e3c6 100644
--- a/Jellyfin.Server.Implementations/Item/LinkedChildrenService.cs
+++ b/Jellyfin.Server.Implementations/Item/LinkedChildrenService.cs
@@ -59,6 +59,27 @@ public class LinkedChildrenService : ILinkedChildrenService
             .ToArray();
     }
 
+    /// <inheritdoc/>
+    public IReadOnlySet<Guid> GetItemsWithAlternateVersions(IReadOnlyList<Guid> itemIds)
+    {
+        if (itemIds.Count == 0)
+        {
+            return new HashSet<Guid>();
+        }
+
+        using var dbContext = _dbProvider.CreateDbContext();
+
+        var parentIds = dbContext.LinkedChildren
+            .Where(lc => (lc.ChildType == DbLinkedChildType.LocalAlternateVersion
+                    || lc.ChildType == DbLinkedChildType.LinkedAlternateVersion)
+                && itemIds.Contains(lc.ParentId))
+            .Select(lc => lc.ParentId)
+            .Distinct()
+            .ToArray();
+
+        return parentIds.ToHashSet();
+    }
+
     /// <inheritdoc/>
     public IReadOnlyDictionary<string, MusicArtist[]> FindArtists(IReadOnlyList<string> artistNames)
     {
-- 
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