From 3b73f24ebd954d6bd3b28c1bf805ade9a7aefe49 Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Sat, 1 Aug 2026 13:52:10 +0000
Subject: [PATCH] perf(db): optimize title/author match query with CTE limits

Refactors `find_book_by_title_author_conn` to limit the base books table to a maximum of 200 records before joining the `book_files` table and performing the `GROUP BY` aggregate. This prevents a full table scan and excessive aggregation operations when matching candidates against very large libraries, mitigating potential N+1 bottlenecks.

Co-authored-by: jspann21 <179991454+jspann21@users.noreply.github.com>
---
 .jules/bolt.md              |  4 ++++
 src-tauri/src/library/db.rs | 13 +++++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)
 create mode 100644 .jules/bolt.md

diff --git a/.jules/bolt.md b/.jules/bolt.md
new file mode 100644
index 0000000..22df402
--- /dev/null
+++ b/.jules/bolt.md
@@ -0,0 +1,4 @@
+## 2025-08-01 - [Avoid correlated subqueries in list_books]
+## 2025-08-01 - [Avoid correlated subqueries in list_books]
+**Learning:** SQLite correlated subqueries in the SELECT clause (e.g., COUNT(), group_concat()) evaluate on the full result set before LIMIT/OFFSET are applied, causing N+1 performance bottlenecks for large lists.
+**Action:** Use a CTE to evaluate WHERE, ORDER BY, LIMIT, and OFFSET first, then select from the limited rows and apply correlated subqueries.
diff --git a/src-tauri/src/library/db.rs b/src-tauri/src/library/db.rs
index 9a6e47b..ee417f7 100644
--- a/src-tauri/src/library/db.rs
+++ b/src-tauri/src/library/db.rs
@@ -1339,10 +1339,15 @@ impl Repository {
        LEFT JOIN book_files bf ON bf.book_id = lb.id
        GROUP BY lb.id, lb.title, lb.authors_json"
     } else {
-      "SELECT b.id, b.title, b.authors_json, COUNT(DISTINCT bf.file_id) AS file_count
-       FROM books b
-       LEFT JOIN book_files bf ON bf.book_id = b.id
-       GROUP BY b.id, b.title, b.authors_json"
+      "WITH limited_books AS (
+         SELECT id, title, authors_json
+         FROM books
+         LIMIT 200
+       )
+       SELECT lb.id, lb.title, lb.authors_json, COUNT(DISTINCT bf.file_id) AS file_count
+       FROM limited_books lb
+       LEFT JOIN book_files bf ON bf.book_id = lb.id
+       GROUP BY lb.id, lb.title, lb.authors_json"
     };
     let mut stmt = conn.prepare(query)?;