From 042d59cff664f6be8a0a372ecbf01e457b41d9ec Mon Sep 17 00:00:00 2001
From: Frederik Ring <frederik.ring@wikimedia.de>
Date: Mon, 15 Jan 2024 16:51:00 +0100
Subject: [PATCH 1/2] fix: add pessimistic lock when fetching next qs batch

---
 app/Http/Controllers/Backend/QsController.php | 1 +
 app/Jobs/CreateQueryserviceBatchesJob.php     | 4 +++-
 app/Jobs/RequeuePendingQsBatchesJob.php       | 1 +
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/app/Http/Controllers/Backend/QsController.php b/app/Http/Controllers/Backend/QsController.php
index 9c5e3af53..3beaa570e 100644
--- a/app/Http/Controllers/Backend/QsController.php
+++ b/app/Http/Controllers/Backend/QsController.php
@@ -19,6 +19,7 @@ public function getBatches(Request $request): \Illuminate\Http\Response
                 ['failed', '=', false]
             ])
                 ->orderBy('id')
+                ->lockForUpdate()
                 ->first();
 
             if ($oldestBatch === null) {
diff --git a/app/Jobs/CreateQueryserviceBatchesJob.php b/app/Jobs/CreateQueryserviceBatchesJob.php
index 1c99abd57..a5a90ead4 100644
--- a/app/Jobs/CreateQueryserviceBatchesJob.php
+++ b/app/Jobs/CreateQueryserviceBatchesJob.php
@@ -77,7 +77,9 @@ private function tryToAppendEntitesToExistingBatches(array $entityIdsFromEvents,
             ['pending_since', '=', null],
             ['failed', '=', false],
             ['wiki_id', '=', $wikiId],
-        ])->get();
+        ])
+            ->lockForUpdate()
+            ->get();
 
         foreach ($notDoneBatches as $qsBatch) {
             $entitiesOnBatch = explode(',', $qsBatch->entityIds);
diff --git a/app/Jobs/RequeuePendingQsBatchesJob.php b/app/Jobs/RequeuePendingQsBatchesJob.php
index 5a6358ba5..d630b65ea 100644
--- a/app/Jobs/RequeuePendingQsBatchesJob.php
+++ b/app/Jobs/RequeuePendingQsBatchesJob.php
@@ -35,6 +35,7 @@ private function markBatchesFailed(): array
                 ['done', '=', false]
             ])
                 ->select('id')
+                ->lockForUpdate()
                 ->get()
                 ->pluck('id')
                 ->toArray();

From 2e9e8310675155803dc6f6d200c2933d0a91203e Mon Sep 17 00:00:00 2001
From: Frederik Ring <frederik.ring@wikimedia.de>
Date: Thu, 18 Jan 2024 15:51:03 +0100
Subject: [PATCH 2/2] feat: ensure child method is only run in transaction

---
 app/Jobs/CreateQueryserviceBatchesJob.php | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/app/Jobs/CreateQueryserviceBatchesJob.php b/app/Jobs/CreateQueryserviceBatchesJob.php
index a5a90ead4..0173aaccd 100644
--- a/app/Jobs/CreateQueryserviceBatchesJob.php
+++ b/app/Jobs/CreateQueryserviceBatchesJob.php
@@ -72,6 +72,12 @@ private function getNewEntities(int $latestCheckpoint): array
 
     private function tryToAppendEntitesToExistingBatches(array $entityIdsFromEvents, int $wikiId): bool
     {
+        if (DB::transactionLevel() < 1) {
+            throw new \Exception(
+                'This method can only be run within the context of a transaction.'
+            );
+        }
+
         $notDoneBatches = QsBatch::where([
             ['done', '=', 0],
             ['pending_since', '=', null],