Problems when warmup procedure and database query procedure running in parallel.

[1528110566]

I want to warmup connection pool when the application start, and I want get some configs from database.
So I wrote this, Test is the name of database table.

@Autowired
private ConnectionPool connectionPool;
@Autowired
private R2dbcEntityTemplate r2dbcEntityTemplate;
@PostConstruct
public void init() {
    connectionPool.warmup().subscribe();
    List<Test> block = r2dbcEntityTemplate.select(Test.class).all().collectList().block();
    System.out.println(block);
}

Expected Behavior

warmup procedure and database query procedure running in parallel, and database query procedure will be waited until there is available connection to use.

Actual Behavior

database query procedure is stuck even if warmup procedure is complete.

Steps to Reproduce

pom.xml

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>spring-boot-starter-parent</artifactId>
        <groupId>org.springframework.boot</groupId>
        <version>2.5.13</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>r2dbc-demo</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-r2dbc</artifactId>
        </dependency>
        <dependency>
            <groupId>dev.miku</groupId>
            <artifactId>r2dbc-mysql</artifactId>
        </dependency>
        <dependency>
            <groupId>io.r2dbc</groupId>
            <artifactId>r2dbc-spi</artifactId>
        </dependency>
        <dependency>
            <groupId>io.r2dbc</groupId>
            <artifactId>r2dbc-pool</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>
    </dependencies>
</project>

java code

@SpringBootApplication
@EnableR2dbcRepositories
public class Application {

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

    @Autowired
    private ConnectionPool connectionPool;
    @Autowired
    private R2dbcEntityTemplate r2dbcEntityTemplate;
    @PostConstruct
    public void init() {
        connectionPool.warmup().subscribe();
        List<Test> block = r2dbcEntityTemplate.select(Test.class).all().collectList().block();
        System.out.println(block);
    }
}

// 1 million records
@Data
@Table("test")
public class Test {
    @Id
    private String name;
}

Possible Solution

change connectionPool.warmup().subscribe(); to connectionPool.warmup().block();
or
add spring.r2dbc.pool.max-acquire-time: 7s in application.yml, after 7 seconds, database query procedure go on and no errors in log file.

Your Environment

• Reactor version(s) used: see pom.xml above
• Other relevant libraries versions (eg. netty, ...): Mysql-5.7.41-winx64
• JVM version (java -version): jdk 1.8.0_162
• OS and version (eg uname -a): windows11 22621.1555