How to enable connection pooling with spring-boot-starter-data-r2dbc?

Question

I have a Spring Boot application with data-r2dbc dependency. I use PostgreSQL as DB.
So I already have in place the following dependencies (gradle notation):

org.springframework.boot:spring-boot-starter-data-r2dbc:2.3.5.RELEASE
io.r2dbc:r2dbc-postgresql

I need to enable connection pooling for R2DBC connections. Unfortunately, I could not find any exhaustive manual to do so.

According to this quite outdated release notes I have to add also io.r2dbc:r2dbc-pool and use spring.r2dbc.pool.* properties to configure pooling.

Also, according to this reference I do not need to turn on pooling manually because SB will enable it if r2dbc-pool is found on the classpath.

Is it enough or do I miss something?

Yes! And the application works. However, I can't be sure that the connection pool is really used. Is there maybe some specific logs that I may spot? Or any other way to verify this? — fyrkov, Dec 15 '20 at 09:43
If you added the dependency there is a pool, with defaults, which you can override through the `spring.r2dbc.pool` properties. As explained in the documentation. — M. Deinum, Dec 15 '20 at 09:44
Can you please point out where is it explained in the documentation? Also I just spotted that the dependency `io.r2dbc:r2dbc-pool` comes already as a transitive dependency from `spring-boot-starter-data-r2dbc:2.3.5.REALEASE` meaning that actually I do not need to declare it explicitly (This can also be seen here: https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-data-r2dbc/2.3.5.RELEASE) — fyrkov, Dec 15 '20 at 11:42
This section explains that it is configured based on the URL (you will need that) everything else is optional. — M. Deinum, Dec 15 '20 at 13:11

score 10 · Accepted Answer · answered Dec 16 '20 at 09:20

Answering my own question.

TLDR

Having org.springframework.boot:spring-boot-starter-data-r2dbc:2.3.5.RELEASE is enough to have connection pooling enabled by default
No need to add io.r2dbc:r2dbc-postgresql explicitly
No need to put :pool: in the URL in this case

Some detailed findings. it seems there are two ways to enable connection pool:

Put :pool: driver chunk into the URL and then io.r2dbc.pool.PoolingConnectionFactoryProvider#create will take care of creating a Connection Pool. This is described at https://github.com/r2dbc/r2dbc-pool#getting-started
Do not have spring.r2dbc.pool.enabled=false in configs (meaning that its absence is interpreted as true by default). This way a Connection Pool will be created by the org.springframework.boot.autoconfigure.r2dbc.ConnectionFactoryConfigurations.Pool#connectionFactory. I am not sure, but it looks like a generalized Spring Boot configuration-style override over a library specific :pool: option.

This options are independent and partly overlap and the second one takes precedence.

The second component evaluates also presence of the :pool: in the URL (see org.springframework.boot.autoconfigure.r2dbc.ConnectionFactoryConfigurations.PooledConnectionFactoryCondition) and if found it delegates the creation of the Connection Pool to the first one.

There is also a peculiar conclusion - having explicit spring.r2dbc.pool.enabled=false leads to creation of a Connection Pool anyway if there is a :pool: in the URL. Therefore the only way to disable pooling is to have spring.r2dbc.pool.enabled=false and to omit :pool: in the URL at the same time.

score 0 · Answer 2 · edited Dec 10 '21 at 22:06

Below code worked for me

String url = "r2dbc:postgres://user:password@hostname:5432/testdb?ApplicationName=myapp";
ConnectionFactory ret= ConnectionFactories.get(url);

ConnectionPoolConfiguration poolConfiguration = ConnectionPoolConfiguration.builder(ret)
                .initialSize(5)                        .maxSize(10).maxIdleTime(Duration.ofMinutes(5)).build();

ConnectionPool pool = new ConnectionPool(poolConfiguration);

return pool;

How to enable connection pooling with spring-boot-starter-data-r2dbc?

2 Answers2