diff --git a/be/.env.example b/be/.env.example
index 8ba78fd4..d2caecf5 100644
--- a/be/.env.example
+++ b/be/.env.example
@@ -20,4 +20,6 @@ DB_DATABASE=
 DB_USERNAME=
 DB_PASSWORD=
 
+CACHE_STORE=file
+
 RECAPTCHA_SECRET=
diff --git a/be/app/Http/Controllers/PostsQuery.php b/be/app/Http/Controllers/PostsQuery.php
index 737e3f89..2834a4e7 100644
--- a/be/app/Http/Controllers/PostsQuery.php
+++ b/be/app/Http/Controllers/PostsQuery.php
@@ -64,9 +64,9 @@ public function query(\Illuminate\Http\Request $request): array
                 ->only(Helper::POST_TYPES_PLURAL)
                 ->flatMap(static fn (Collection $posts) => $posts->pluck('authorUid'))
                 ->concat($latestRepliers->pluck('uid'))
-                ->filter()->unique()->toArray() // remove NULLs
+                ->filter()->unique() // remove NULLs
         )->with(['currentForumModerator' => $whereCurrentFid, 'currentAuthorExpGrade' => $whereCurrentFid])
-            ->selectPublicFields()->get()->toArray();
+            ->selectPublicFields()->get();
         Debugbar::stopMeasure('queryUsers');
 
         return [
@@ -75,7 +75,7 @@ public function query(\Illuminate\Http\Request $request): array
                 ...$query->getResultPages(),
                 ...Arr::except($result, ['fid', ...Helper::POST_TYPES_PLURAL])
             ],
-            'forum' => Forum::fid($result['fid'])->selectPublicFields()->first()?->toArray(),
+            'forum' => Forum::fid($result['fid'])->selectPublicFields()->first(),
             'threads' => $query->reOrderNestedPosts($query::nestPostsWithParent(...$result)),
             'users' => $users,
             'latestRepliers' => $latestRepliers
diff --git a/be/app/Http/Controllers/ThreadsSitemap.php b/be/app/Http/Controllers/ThreadsSitemap.php
index 6f48da41..cc7bd1a2 100644
--- a/be/app/Http/Controllers/ThreadsSitemap.php
+++ b/be/app/Http/Controllers/ThreadsSitemap.php
@@ -6,22 +6,24 @@
 use App\Eloquent\Model\Post\PostFactory;
 use App\Helper;
 use Illuminate\Http;
+use Illuminate\Support\Facades\Cache;
 
 class ThreadsSitemap extends Controller
 {
-    public static int $maxItems = 50000;
+    public static int $maxUrls = 50000;
 
     public function query(Http\Request $request, int $fid): Http\Response
     { // https://stackoverflow.com/questions/59554777/laravel-how-to-set-default-value-in-validator-at-post-registeration/78707950#78707950
         ['cursor' => $cursor] = $request->validate([
             'cursor' => 'integer'
         ]) + ['cursor' => 0];
-        Helper::abortAPIIfNot(40406, (new Forum())->fid($fid)->exists());
+        Helper::abortAPIIfNot(40406, Forum::fid($fid)->exists());
 
-        return Helper::xmlResponse(view('sitemaps.threads', [
-            'tids' => PostFactory::newThread($fid)
-                ->where('tid', '>', $cursor)->limit(self::$maxItems)
-                ->orderByDesc('tid')->pluck('tid')
-        ]));
+        return Cache::remember("/sitemaps/forums/$fid/threads?cursor=$cursor", 86400,
+            static fn () => Helper::xmlResponse(view('sitemaps.threads', [
+                'tids' => PostFactory::newThread($fid)
+                    ->where('tid', '>', $cursor)->limit(self::$maxUrls)
+                    ->orderBy('tid')->pluck('tid')
+            ])));
     }
 }
diff --git a/be/app/Http/Controllers/UsersQuery.php b/be/app/Http/Controllers/UsersQuery.php
index 3bdcc430..64e56d55 100644
--- a/be/app/Http/Controllers/UsersQuery.php
+++ b/be/app/Http/Controllers/UsersQuery.php
@@ -19,7 +19,7 @@ public function query(\Illuminate\Http\Request $request): array
         ]);
         Helper::abortAPIIf(40402, empty($queryParams));
 
-        $queryBuilder = (new User())->newQuery();
+        $queryBuilder = User::newQuery();
 
         $nullableParams = ['name', 'displayName', 'gender'];
         foreach ($nullableParams as $nullableParamName) {
diff --git a/be/app/Http/PostsQuery/IndexQuery.php b/be/app/Http/PostsQuery/IndexQuery.php
index a478cac0..a6b98ac0 100644
--- a/be/app/Http/PostsQuery/IndexQuery.php
+++ b/be/app/Http/PostsQuery/IndexQuery.php
@@ -41,15 +41,16 @@ public function query(QueryParams $params, ?string $cursor): self
                 ->only($postTypes)
                 ->transform(static fn (Post $model, string $type) => $model->selectCurrentAndParentPostID());
         $getFidByPostIDParam = static function (string $postIDName, int $postID): int {
-            $fids = Forum::get('fid')->pluck('fid')->toArray();
-            $counts = collect($fids)
+            $counts = Forum::get('fid')
+                ->pluck('fid')
                 ->map(static fn (int $fid) =>
                     PostFactory::getPostModelsByFid($fid)[Helper::POST_ID_TO_TYPE[$postIDName]]
                         ->selectRaw("{$fid} AS fid, COUNT(*) AS count")
                         ->where($postIDName, $postID))
                 ->reduce(static fn (?BuilderContract $acc, EloquentBuilder|QueryBuilder $cur): BuilderContract =>
                     $acc === null ? $cur : $acc->union($cur))
-                ->get()->where('count', '!=', 0);
+                ->get()
+                ->where('count', '!=', 0);
             Helper::abortAPIIf(50001, $counts->count() > 1);
             Helper::abortAPIIf(40401, $counts->count() === 0);
             return $counts->pluck('fid')->first();
@@ -57,7 +58,7 @@ public function query(QueryParams $params, ?string $cursor): self
 
         if (\array_key_exists('fid', $flatParams)) {
             /** @var int $fid */ $fid = $flatParams['fid'];
-            if ((new Forum())->fid($fid)->exists()) {
+            if (Forum::fid($fid)->exists()) {
                 /** @var Collection<string, EloquentBuilder<Post>> $queries key by post type */
                 $queries = $getQueryBuilders($fid);
             } elseif ($hasPostIDParam) { // query by post ID and fid, but the provided fid is invalid
diff --git a/be/routes/api.php b/be/routes/api.php
index 1b87d2ca..3924fc9e 100644
--- a/be/routes/api.php
+++ b/be/routes/api.php
@@ -4,7 +4,7 @@
 use App\Http\Middleware\ReCAPTCHACheck;
 use Illuminate\Support\Facades\Route;
 
-Route::get('/forums', static fn () => \App\Eloquent\Model\Forum::all()->toArray());
+Route::get('/forums', static fn () => \App\Eloquent\Model\Forum::all());
 Route::middleware(ReCAPTCHACheck::class)->group(static function () {
     Route::get('/posts', [Controllers\PostsQuery::class, 'query']);
     Route::get('/users', [Controllers\UsersQuery::class, 'query']);
diff --git a/be/routes/web.php b/be/routes/web.php
index dd467426..69ed6f09 100644
--- a/be/routes/web.php
+++ b/be/routes/web.php
@@ -5,12 +5,13 @@
 use App\Helper;
 use App\Http\Controllers;
 
-Route::get('/sitemaps/forums', static fn() => Helper::xmlResponse(view('sitemaps.forums', [
-    'tidsKeyByFid' => (new Forum())->get('fid')->pluck('fid')->mapWithKeys(fn(int $fid) => [
-        $fid => DB::query()
-            ->fromSub(PostFactory::newThread($fid)
-                ->selectRaw('ROW_NUMBER() OVER (ORDER BY tid DESC) AS rn, tid'), 't')
-            ->whereRaw('rn % ' . Controllers\ThreadsSitemap::$maxItems . ' = 0')
-            ->pluck('tid')
-    ])])));
+Route::get('/sitemaps/forums', static fn () => Cache::remember('/sitemaps/forums', 86400,
+    static fn () => Helper::xmlResponse(view('sitemaps.forums', [
+        'tidsKeyByFid' => Forum::get('fid')->pluck('fid')->mapWithKeys(fn (int $fid) => [
+            $fid => DB::query()
+                ->fromSub(PostFactory::newThread($fid)
+                    ->selectRaw('ROW_NUMBER() OVER (ORDER BY tid DESC) AS rn, tid'), 't')
+                ->whereRaw('rn % ' . Controllers\ThreadsSitemap::$maxUrls . ' = 0')
+                ->pluck('tid')
+        ])]))));
 Route::get('/sitemaps/forums/{fid}/threads', [Controllers\ThreadsSitemap::class, 'query']);