Database connection leak with SseEmitter

I have a problem with a database connection pool in Spring Boot 2, where connections are not returned to the pool even though they are neatly wrapped in @Transactional.

Upon opening the home page, I run a query and then open an SSE stream:

    @GetMapping("")
    public SseEmitter home() {
      derpService.derp();
      return obs.subscribeSse();
    }

The derp() call looks like this:

    @Transactional
    void derp() {
        derpRepository.derp();
    }

Which leads to:

    @Query(value = "SELECT 'derp'", nativeQuery = true)
    void derp();

As long as the SSE stream is open, the connection from the derp() call is not released. This goes against my intuition, because I assumed @Transactional would return the connection as soon as the flow exits the transaction scope.

Is this a bug in Spring?

Steps to reproduce

1. Open the minimal example (link below)
2. Run docker-compose up -d --build
3. Start the application
4. Open http://localhost:8088 in six tabs
5. The sixth tab will not load because all connections are in use.

Resources

• Minimal example on https://github.com/Oduig/connectionleak.
• SO question on https://stackoverflow.com/questions/49071931/database-connection-leak-in-spring-boot-with-sseemitter

[Divine1]

@bclozel thank you, i think its the same problem not different

spring.jpa.open-in-view = false

adding above property fixed the issue. it detaches the dbconnectionSession from the incoming session.

references

• https://developer.jboss.org/docs/DOC-13954
• https://stackoverflow.com/questions/30549489/what-is-this-spring-jpa-open-in-view-true-property-in-spring-boot

[bclozel]

If you’re starting a transaction, a streaming query or if the session is configured to stay opened with the view, you are effectively binding that database resource to the persistent connection. If you believe you’ve found a different problem, please create a new issue with a sample, minimal project that reproduces the behavior.