Prevent concurrency issues on small system

Serializable isolation level is not really useful for a job system,
where we insert/update many rows

server/core/helpers/database-utils.ts

@@ -68,11 +68,14 @@ export function transactionRetryer<T> (func: (err: any, data: T) => any) {
   })
 }
 
-export function saveInTransactionWithRetries<T extends Pick<Model, 'save' | 'changed'>> (model: T) {
+export function saveInTransactionWithRetries<T extends Pick<Model, 'save' | 'changed'>> (
+  model: T,
+  isolationLevel: Transaction.ISOLATION_LEVELS = Transaction.ISOLATION_LEVELS.SERIALIZABLE
+) {
   const changedKeys = model.changed() || []
 
   return retryTransactionWrapper(() => {
-    return sequelizeTypescript.transaction(async transaction => {
+    return sequelizeTypescript.transaction({ isolationLevel }, async transaction => {
       try {
         await model.save({ transaction })
       } catch (err) {

server/core/lib/runners/job-handlers/abstract-job-handler.ts

@@ -28,6 +28,7 @@ import { PeerTubeSocket } from '@server/lib/peertube-socket.js'
 import { RunnerJobModel } from '@server/models/runner/runner-job.js'
 import { setAsUpdated } from '@server/models/shared/update.js'
 import { MRunnerJob } from '@server/types/models/runners/index.js'
+import { Transaction } from 'sequelize'
 
 type CreateRunnerJobArg =
   | {
@@ -98,7 +99,7 @@ export abstract class AbstractJobHandler<C, U extends RunnerJobUpdatePayload, S
       priority
     })
 
-    await saveInTransactionWithRetries(runnerJob)
+    await saveInTransactionWithRetries(runnerJob, Transaction.ISOLATION_LEVELS.READ_COMMITTED)
 
     if (runnerJob.state === RunnerJobState.PENDING) {
       PeerTubeSocket.Instance.sendAvailableJobsPingToRunners()