Heroku Postgres：此连接已关闭

我开发了一个小型 Heroku + Grails + Postreg 应用程序。部署后 20 分钟左右它就会正常工作，之后我总是得到：

 This connection has been closed.. Stacktrace follows: Heroku/myapp
- org.postgresql.util.PSQLException: This connection has been closed. Heroku/myapp
- at org.postgresql.jdbc2.AbstractJdbc2Connection.checkClosed(AbstractJdbc2Connection.java:837) Heroku/myapp
- at org.postgresql.jdbc2.AbstractJdbc2Connection.getAutoCommit(AbstractJdbc2Connection.java:798) Heroku/myapp
- at org.grails.datastore.gorm.GormStaticApi$_methodMissing_closure2.doCall(GormStaticApi.groovy:102) Heroku/myapp
- at com.myapp.WorkspaceController.list(WorkspaceController.groovy:18) Heroku/myapp
- at grails.plugin.cache.web.filter.PageFragmentCachingFilter.doFilter(PageFragmentCachingFilter.java:198) Heroku/myapp
- at grails.plugin.cache.web.filter.AbstractFilter.doFilter(AbstractFilter.java:63) Heroku/myapp
- at grails.plugin.springsecurity.web.filter.GrailsAnonymousAuthenticationFilter.doFilter(GrailsAnonymousAuthenticationFilter.java:53) Heroku/myapp
- at grails.plugin.springsecurity.web.authentication.RequestHolderAuthenticationFilter.doFilter(RequestHolderAuthenticationFilter.java:53) Heroku/myapp
- at grails.plugin.springsecurity.web.authentication.logout.MutableLogoutFilter.doFilter(MutableLogoutFilter.java:62) Heroku/myapp
- at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) Heroku/myapp
- at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) Heroku/myapp
- at java.lang.Thread.run(Thread.java:745) Heroku/myapp
- 2015-08-07 15:11:10,685 [http-nio-20850-exec-5] ERROR spi.SqlExceptionHelper - This connection has been closed. Heroku/myapp
- 2015-08-07 15:11:10,689 [http-nio-20850-exec-5] ERROR spi.SqlExceptionHelper - This connection has been closed. Heroku/myapp
- 2015-08-07 15:11:10,696 [http-nio-20850-exec-5] ERROR errors.GrailsExceptionResolver - PSQLException occurred when processing request: [GET] /api/users/21/workspaces Heroku/myapp
- This connection has been closed.. Stacktrace follows: Heroku/myapp

我自己解决了这个问题，将其添加到 DataSource.groovy 中：

dataSource {
    pooled = true
    properties {
       maxActive = -1
       minEvictableIdleTimeMillis=1800000
       timeBetweenEvictionRunsMillis=1800000
       numTestsPerEvictionRun=3
       testOnBorrow=true
       testWhileIdle=true
       testOnReturn=true
       validationQuery="SELECT 1"
    }
}