From 0368791850ef05336f0121e96c2605f7e7933173 Mon Sep 17 00:00:00 2001
From: Application-drop-up <msts.oo0131@gmail.com>
Date: Fri, 22 May 2026 09:04:49 +0900
Subject: [PATCH] perf: add index on site_state_parties.world_heritage_site_id
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The composite PK (state_party_code, world_heritage_site_id) cannot satisfy
WHERE world_heritage_site_id IN (...) queries efficiently — MySQL falls back
to a full table scan on every countries eager load.

Adding a standalone index eliminates the full scan and turns the eager load
into an index seek, directly reducing list and search endpoint latency.

Closes #464
Part of #463
---
 ...e_state_parties_world_heritage_site_id.php | 22 +++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 src/database/migrations/2026_05_22_000001_add_index_to_site_state_parties_world_heritage_site_id.php

diff --git a/src/database/migrations/2026_05_22_000001_add_index_to_site_state_parties_world_heritage_site_id.php b/src/database/migrations/2026_05_22_000001_add_index_to_site_state_parties_world_heritage_site_id.php
new file mode 100644
index 0000000..13c8bc1
--- /dev/null
+++ b/src/database/migrations/2026_05_22_000001_add_index_to_site_state_parties_world_heritage_site_id.php
@@ -0,0 +1,22 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('site_state_parties', function (Blueprint $table) {
+            $table->index('world_heritage_site_id', 'idx_ssp_world_heritage_site_id');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('site_state_parties', function (Blueprint $table) {
+            $table->dropIndex('idx_ssp_world_heritage_site_id');
+        });
+    }
+};