Play Scala JDBC Config

<app>-<models>DatabaseExecutionContext.scala

package models

import javax.inject._

import akka.actor.ActorSystem
import play.api.libs.concurrent.CustomExecutionContext

/**
 * This class is a pointer to an execution context configured to point to "database.dispatcher"
 * in the "application.conf" file.
 */
@Singleton
class DatabaseExecutionContext @Inject()(system: ActorSystem) extends CustomExecutionContext(system, "database.dispatcher")

application.conf

# Default database configuration using H2 database engine in a persistent mode
db.default.driver=org.h2.Driver
db.default.url="jdbc:h2:target/db"

# db connections = ((physical_core_count * 2) + effective_spindle_count)
# https://github.com/brettwooldridge/HikariCP/wiki/About-Pool-Sizing
fixedConnectionPool = 9

database.dispatcher {
  executor = "thread-pool-executor"
  throughput = 1
  thread-pool-executor {
    fixed-pool-size = ${fixedConnectionPool}
  }
}

// https://github.com/playframework/play-samples/tree/2.8.x/play-scala-anorm-example

ScalaApplicationDatabase.scala

// https://www.playframework.com/documentation/2.8.x/AccessingAnSQLDatabase

import javax.inject.Inject
import play.api.db.Database

import scala.concurrent.Future

class ScalaApplicationDatabase @Inject() (db: Database, databaseExecutionContext: DatabaseExecutionContext) {
  def updateSomething(): Unit = {
    Future {
      db.withConnection { conn =>
        // do whatever you need with the db connection
      }
    }(databaseExecutionContext)
  }
}