Using read-only DataSource in Play with Play-Ebean plugin

[michae...@lookout.com]

Hi,

I'm interested in using the read-only datasource feature added by https://github.com/ebean-orm/ebean/issues/1232.  I'm using Play Framework with the Play-Ebean plugin and HikariCP for connection pooling.  I can't quite figure out how to enable the read-only feature, though.  Since I'm not explicitly creating my default datasource (i.e. I'm handling it through config), I'm not sure where to hook in and setup the read-only datasource.  Any suggestions?

Thanks,

Mike

[Rob Bygrave]

>  hook in and setup the read-only datasource

On DatabaseConfig we call databaseConfig.setReadOnlyDataSource() passing the DataSource. Noting this DataSource should be autoCommit=true.

https://ebean.io/apidoc/12/io/ebean/config/DatabaseConfig.html#setReadOnlyDataSource(javax.sql.DataSource)

Ebean will then automatically use that DataSource when queries are executed outside of an explicit transaction.  Also when we use @Transactional(readOnly=true) that will  also use the read only DataSource.

Note that there is a performance benefit of using the read-only DataSource even when hitting the same database (rather than a read replica database) due to the ability to use autoCommit=true [more noticeable when there are lots of fast queries].

> HikariCP for connection pooling

Just a note to say that a team I am working in has migrated away from HikariCP to Ebean's pool due to Ebean's pool being more robust at handling RDS instance upgrade/failover. That is, one of the nice tricks in the Ebean pool is that it validates on error (and in the background) - it hence does not need any validate on borrow/return. This approach makes the ebean pool very robust and also fast.  That plus it auto-sizes itself and is fast due to the simple but fast internal "array slot" style buffer.  Anyway, by all means use HikariCP but note that I am comfortable stating that Ebean's DataSource is in my observations more robust and definitely what I recommend to people.

Fun fact, Ebean's DataSource implementation is actually older than Ebean at around 18 years old - Ebean is around 15 years old.

Cheers, Rob.

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[Michael Mole]

Thanks for the info, and I'll definitely consider using Ebean's pool!

One followup question - Do you know what the Play/Guice mechanism is for getting access to the DatabaseConfig object?

Thanks again,

Mike

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Mike Molé (he/him/his)
Senior Staff Software Engineer
michae...@lookout.com | +1-908-770-0816 | www.lookout.com

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[Rob Bygrave]

> Do you know what the Play/Guice mechanism is for getting access to the DatabaseConfig object?

No  I don't.  I am hoping there is another helpful person that can jump in and help with that.

Cheers, Rob.

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[michae...@lookout.com]

I figured out what to do.  If you're using the Play-Ebean plugin, you need to implement https://github.com/payintech/play-ebean/blob/master/play-ebean/src/main/java/play/db/ebean/orm/EbeanServerExtraConfig.java.  Then register the fully qualified classname in the extra-config section as described here, https://github.com/payintech/play-ebean/blob/master/README.md#configure-the-module.  This will allow you to programmatically adjust the config before the Ebean server objects are created.

The other hiccup I encountered was that I used Play configuration to create a read-only Hikari pool/datasource.  Since the EbeanServerExtraConfig does not support injecting that dependency, I accessed it via JNDI instead.

For example:

public class CustomEbeanServerExtraConfig implements EbeanServerExtraConfig {

    private static final Logger.ALogger logger = Logger.of(CustomEbeanServerExtraConfig.class);

    @Override

    public void applyExtraConfiguration(ServerConfig ebeanServerConfig, Config playConfig) {

        try {

            DataSource roDs = (DataSource) play.api.libs.JNDI.initialContext().lookup("readOnly");

            ebeanServerConfig.setReadOnlyDataSource(roDs);

            logger.info("Configured read-only datasource");

        } catch (NamingException e) {

            logger.warn("Unable to configure read-only datasource");

        }

    }

}

---

(from application.conf)

      # Extra Ebean server configuration

      # Use full classpath (ie: ebean.DemoEbeanServerExtraConfig)

      extra-config = [

        db.CustomEbeanServerExtraConfig

      ]

---

(from my env-specific application.conf extension)

db {

  default {

    driver = "org.mariadb.jdbc.Driver"

    url = "jdbc:mysql://<aws-aurora-writer-endpoint>:3306/mydb"

    username = <redacted>

  }

  readOnly {

    driver = "org.mariadb.jdbc.Driver"

    url = "jdbc:mysql://<aws-aurora-reader-endpoint>:3306/mydb"

    username = <redacted>

    readOnly = true

    jndiName = readOnly

  }

}

[Rob Bygrave]

Excellent.  Thanks for posting back those details, that will help others down the track.

Cheers, Rob. 

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