A few words about R2DBC and PostgreSQL

• Reactive programming is more difficult to debug
• Developing reactive systems is more difficult than classic, blocking ones; if you unintentionally block the thread, you are finished. That is why the project appeared (one of the authors -bsideup )
• Reactive programming, and in particular elasticity, is needed mainly at high loads a la Netflix. If you have 100 RPS, you should probably write code in a blocking style - it's cheaper and easier

1. https://github.com/jasync-sql/jasync-sql - asynchronous driver for PostgreSQL, written in Kotlin, where Netty is the transport
2. The solution Vert.x uses is https://github.com/mauricio/postgresql-async . It is noteworthy that the project is archived, and the previous jasync-sql driver rewrites just the same (though, the original is written in Scala, and the new solution is written in Kotlin).
   Update I was corrected in the comments, the client from Vert.x is alive and feels good in benchmarks .
   
3. The driver from the Spring team is https://github.com/r2dbc/r2dbc-postgresql . This driver immediately provides a reactive API (and not asynchronous), and Netty is used for transport, as in jasync-sql.

• https://www.postgresql.org/docs/current/libpq-async.html
• https://www.postgresql.org/docs/current/libpq-notify.html

spring.r2dbc.username=postgres
spring.r2dbc.password=P4$$W0RddD
spring.r2dbc.url=r2dbc:postgresql://localhost:5432/r2dbc
spring.r2dbc.pool.enabled=true
spring.r2dbc.pool.initial-size=10
spring.r2dbc.pool.max-idle-time=1m
spring.r2dbc.pool.max-size=30
spring.data.r2dbc.repositories.enabled=true

public class Customer {
    @Id
    private Long id;

    private String firstName;

    private String lastName;

    public Customer(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }
}

public interface CustomerRepository extends ReactiveCrudRepository<Customer, Long> {
}

@RestController
@RequestMapping("/")
public class CustomerController {

    private CustomerRepository customerRepository;

    @PostMapping("/customer")
    Mono<Void> create(@RequestBody Publisher<Customer> customerFlux) {
        return customerRepository.saveAll(customerFlux).then();
    }

    @GetMapping("/customer")
    public Flux<Customer> list() {
        return customerRepository.findAll();
    }

    @GetMapping("/customer/{id}")
    public Mono<Customer> findById(@PathVariable Long id) {
        return customerRepository.findById(id);
    }
}