Default HikariCP connection pool starting Spring Boot application

Question

I'm using version: 2.1.6.RELEASE form Spring Boot in my pom.xml-dependencies. To connect to my database I put following in application.properties:

spring.datasource.url= jdbc:postgresql://
spring.datasource.username=
spring.datasource.password=

When checking the amount of connections in postgresql with:

SELECT * FROM pg_stat_activity;

I see each time I start the application exactly 10 connections are made. They almost all have the same query:

SET application_name = 'PostgreSQL JDBC Driver'

Is there a way to prevent the application of making that many connections? Should I make my own pool-configuration? What resource in my Java-application does initialize these connections?

The only thing I can think of is that I create EntityManager(s) with the @Autowired annotation, EntityManager from:

javax.persistence.EntityManager;

But I read you should only close the connection this makes when using an EntityManagerFactory. The annotation should close the connection.

If you would require more info, I could edit my post

score 7 · Answer 1 · edited Jun 20 '20 at 09:12

HikariCP opens 10 idle connections by default,

Default: 10

You can override minimumIdle which is less recommended

HikariCP will make a best effort to add additional connections quickly and efficiently. However, for maximum performance and responsiveness to spike demands, we recommend not setting this value and instead allowing HikariCP to act as a fixed size connection pool. Default: same as maximumPoolSize

Or maximumPoolSize, but it effect the maximum size of connection pool

This property controls the maximum size that the pool is allowed to reach, including both idle and in-use connections.

score 5 · Accepted Answer · answered Aug 08 '19 at 13:31

5

That's no a connection leak but the desired behavior. Spring Boot Data uses HikariCP as a connection pool.

You can configure the max pool size as property. For example:

spring.datasource.hikari.maximum-pool-size=5

answered Aug 08 '19 at 13:31

Simon Martinelli

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Could i set this to 1? Why would you default need 10 connections? Can lowering this amount be a problem? – SimonartM Aug 08 '19 at 13:33
1

That doesn't make sense. Why do you think that 10 connections are a lot? – Simon Martinelli Aug 08 '19 at 13:36
Does each thread use a different connection? What's the point having 10 connections? – SimonartM Aug 08 '19 at 13:37
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The reason is performance. And yes each thread that want's to access the database will be a connection assigned. HikariCP is very fast in dealing with the connections. The size of the pool depends on the number of concurrent users your application will have. – Simon Martinelli Aug 08 '19 at 13:40
Thank you very much for this explanation – SimonartM Aug 08 '19 at 13:41

score 1 · Answer 3 · edited Jun 26 '21 at 00:27

1

HikariCP has a maximum of 10 connections by default.

You can configure the maximum pool size like so:

spring.datasource.hikari.maximum-pool-size=5

To enable tracing logs:

logging.level.com.zaxxer.hikari.HikariConfig=DEBUG
logging.level.com.zaxxer.hikari=TRACE

edited Jun 26 '21 at 00:27

Carl Düvel

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answered Jun 25 '21 at 12:31

Amit Nayak

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Default HikariCP connection pool starting Spring Boot application

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