Custom AsyncExecutor for Database.forConfig

application.conf

slick.dbs.default {
  profile = "foo.bar.PostgresProfile$"
  
  db {
    poolName = "slick-default-db"
    url = ${?DB_URL}
    user = ${?DB_USER}
    password = ${?DB_PASSWORD}
    numThreads = 20
    minConnections = 5
    maxConnections = 20
  }
}

CustomExecutorJdbcBackend.scala

package foo.bar

import java.sql.{ Array => _, _ }

import com.typesafe.config.{ Config, ConfigFactory }
import slick.jdbc.{ JdbcBackend, JdbcDataSource }
import slick.util.ConfigExtensionMethods._
import slick.util.{ AsyncExecutor, ClassLoaderUtil }

trait CustomExecutorJdbcBackend extends JdbcBackend {
  override val Database = new DatabaseFactoryDef {}

  trait DatabaseFactoryDef extends super.DatabaseFactoryDef {
    override def forConfig(
      path: String,
      config: Config = ConfigFactory.load(),
      driver: Driver = null,
      classLoader: ClassLoader = ClassLoaderUtil.defaultClassLoader
    ): Database = {
      val usedConfig: Config = if (path.isEmpty) config else config.getConfig(path)
      val source = JdbcDataSource.forConfig(usedConfig, driver, path, classLoader)
      val poolName = usedConfig.getStringOr("poolName", path)
      val numThreads = usedConfig.getIntOr("numThreads", 20)
      val maxConnections = source.maxConnections.fold(numThreads * 5)(identity)
      val registerMbeans = usedConfig.getBooleanOr("registerMbeans", false)
      
      // Use a custom async executor class:
      val executor = SomeCustomAsyncExecutor(poolName, numThreads, numThreads, usedConfig.getIntOr("queueSize", 1000),
        maxConnections, registerMbeans = registerMbeans)
      forSource(source, executor)
    }
  }
}

object CustomExecutorJdbcBackend extends CustomExecutorJdbcBackend

PostgresProfile.scala

package foo.bar

import com.github.tminglei.slickpg._

trait PostgresProfile extends ExPostgresProfile
  with PgDateSupportJoda
  with PgDate2Support
  with PgArraySupport
  with PgEnumSupport
  with PgRangeSupport
  with PgHStoreSupport {
    
    // [...]
    // other profile content, cusotmized API etc.
}

// Must use an early definitions block to set the backend
object PostgresProfile extends {
  override val backend = CustomExecutorJdbcBackend
} with PostgresProfile