use iterator to reduce cache in migration

3 jobs for improve-source in 3 minutes and 29 seconds (queued for 3 seconds)
latest
Status Name Job ID Coverage
  Build
passed build-backend #128526
k8s

00:02:24

passed build-frontend #128527
k8s

00:01:22

 
  Test
passed test-backend #128528

00:01:04