SpringBoot r2dbcrepository always run in single thread

package com.example;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class R2DBCApplication {
    private static final Logger log = LoggerFactory.getLogger(R2DBCApplication.class);

    public static void main(final String[] args) {
        SpringApplication.run(R2DBCApplication.class, args);
    }

}

package com.example;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import reactor.core.publisher.Mono;

import java.util.UUID;

@RestController
public class ValueController {
    private static final Logger log = LoggerFactory.getLogger(ValueController.class);

    @Autowired
    private ValueRepository repository;

    @GetMapping("/value")
    public Mono<String> get() {
        final var uuid = UUID.randomUUID().toString();
        log.info("start for uuid = {}", uuid);
        return repository
                .findById(1L)
                .map(ValueEntity::getId)
                .map(String::valueOf)
                .switchIfEmpty(Mono.fromSupplier(() -> uuid))
                .doOnNext(v -> log.info("after switchIfEmpty uuid = {}", v))
                .doOnNext(v -> log.info("breakpoint uuid = {}", v));
    }
}

package com.example;

import org.springframework.data.annotation.Id;
import org.springframework.data.relational.core.mapping.Column;
import org.springframework.data.relational.core.mapping.Table;

@Table("value")
public class ValueEntity {

    @Id
    @Column("id")
    private Long id;

    @Column("value")
    private String value;

    public Long getId() {
        return id;
    }

    public void setId(final Long id) {
        this.id = id;
    }

    public String getValue() {
        return value;
    }

    public void setValue(final String value) {
        this.value = value;
    }
}

package com.example;

import org.springframework.data.r2dbc.repository.R2dbcRepository;

public interface ValueRepository extends R2dbcRepository<ValueEntity, Long> {

}

server.port: 9080
spring:
  application.name: r2dbc-service
  r2dbc:
    url: r2dbc:postgresql://localhost:5433/postgres
    username: postgres
    password: 12345
    properties:
      schema: public

logging.level.root: DEBUG

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.0.2</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>17</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-r2dbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>r2dbc-postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>