The individual items in chunks in the typical can also in principle be processed concurrently. In this case the transaction boundary has to move to the level of the individual item, so that each transaction is on a single thread:

1   |  REPEAT(until=exhausted, exception=not critical) {
|
2   |    REPEAT(size=5, concurrent) {
|
3   |      TX {
4   |        RETRY(stateful, exception=deadlock loser) {
4.1 |          input;
5   |        } PROCESS {
|          output;
6   |        } RECOVER {
|          recover;
|        }
|      }
|
|    }
|
|  }
		

This plan sacrifices the optimisation benefit, that the simple plan had, of having all the transactional resources chunked together. It is only useful if the cost of the processing (5) is much higher than the cost of transaction management (3).