How to configure connection pool in Spring Boot - spring-boot

Question

How to configure my Spring Boot service to have max 2 open connections to the Postgres database? Application is used on the PRODUCTION only by a few people and I don't want to
my pom:
(...)
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.8.RELEASE</version>
<relativePath/>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.datatype</groupId>
<artifactId>jackson-datatype-hibernate5</artifactId>
</dependency>
<dependency>
<groupId>commons-lang</groupId>
<artifactId>commons-lang</artifactId>
<version>2.6</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.postgresql</groupId>
<artifactId>postgresql</artifactId>
<version>9.4-1200-jdbc41</version>
<scope>provided</scope>
<exclusions>
<exclusion>
<artifactId>slf4j-simple</artifactId>
<groupId>org.slf4j</groupId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-log4j2</artifactId>
</dependency>
<dependency>
<groupId>com.caucho</groupId>
<artifactId>hessian</artifactId>
<version>4.0.51</version>
</dependency>
<dependency>
<groupId>com.vladmihalcea</groupId>
<artifactId>hibernate-types-52</artifactId>
<version>2.4.3</version>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-api</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-api</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
(...)
</build>
</project>
and my application.properties file:
spring.datasource.url=jdbc:postgresql://xxx
spring.datasource.username=xxx
spring.datasource.password=xxx
spring.datasource.maximum-pool-size=2 //I think it is not sufficient
info.app.name: xxx
I think spring.datasource.maximum-pool-size=2 is not sufficient. What should I add to the properties file? Should I maybe exclude HikariCP from my pom file?

Answer 1

Since Spring Boot 2.0, Hikari is the default DataSource implementation. Therefore, if you want to configure the maximumPoolSize (a parameter for Hikeri Configuration) in Spring Boot, you are supposed to set it as follows:
For application.properties
spring.datasource.hikari.maximum-pool-size=2
For application.yml
spring:
datasource:
hikari:
maximum-pool-size: 2

Answer 2

If you haven't changed the connection implementation pool that Spring is using, it should be HikariCP, and then the setting you're looking for is:
spring.datasource.hikari.maximum-pool-size
its listed here: https://docs.spring.io/spring-boot/docs/current/reference/html/appendix-application-properties.html