expected rows per company: 250

no lock, READ COMMITTED:
  run1: committed, waited 0.0s, deleted 250
  run2: committed, waited 0.0s, deleted 0
  rows afterwards: 500
xact lock, READ COMMITTED:
  run1: committed, waited 0.0s, deleted 250
  run2: committed, waited 0.7s, deleted 250
  rows afterwards: 250
xact lock, REPEATABLE READ:
  run1: committed, waited 0.0s, deleted 250
  run2: SerializationFailure
  rows afterwards: 250
no lock, REPEATABLE READ:
  run1: committed, waited 0.0s, deleted 250
  run2: SerializationFailure
  rows afterwards: 250
no lock, SERIALIZABLE:
  run1: committed, waited 0.0s, deleted 250
  run2: SerializationFailure
  rows afterwards: 250
no lock, READ COMMITTED, new company:
  run1: committed, waited 0.0s, deleted 0
  run2: committed, waited 0.0s, deleted 0
  rows afterwards: 500
no lock, REPEATABLE READ, new company:
  run1: committed, waited 0.0s, deleted 0
  run2: committed, waited 0.0s, deleted 0
  rows afterwards: 500
no lock, SERIALIZABLE, new company:
  run1: committed, waited 0.0s, deleted 0
  run2: SerializationFailure
  rows afterwards: 250
xact lock, READ COMMITTED, new company:
  run1: committed, waited 0.0s, deleted 0
  run2: committed, waited 0.7s, deleted 250
  rows afterwards: 250

kill the holder after its delete, before its commit; a second run waits; an observer counts rows every 20 ms
  holder: OperationalError
  waiter: committed, waited 0.6s, deleted 250
  row counts the observer ever saw: [250]; final rows: 250

the idle-in-transaction timeout (1 s) ends a run that sits idle 3 s inside its company transaction
  run fails with OperationalError; rows afterwards: 250
  next run: committed, waited 0.0s, deleted 250; rows afterwards: 250