我已经建立了从 localhost 到 Heroku 上的 Dev 数据库的连接（如：Heroku 上的进化错误中所述），并且在尝试应用进化几次后我收到以下错误：
SQLException: Unable to open a test connection to the given database. JDBC url = [URL], username = null. Terminating connection pool.
Original Exception: org.postgresql.util.PSQLException: FATAL: too many connections for role "ntnkypawxazhwo"
at org.postgresql.core.v3.ConnectionFactoryImpl.readStartupMessages(ConnectionFactoryImpl.java:469)
at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:110)
at org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:64)
at org.postgresql.jdbc2.AbstractJdbc2Connection.<init>(AbstractJdbc2Connection.java:123)
at org.postgresql.jdbc3.AbstractJdbc3Connection.<init>(AbstractJdbc3Connection.java:28)
at org.postgresql.jdbc3g.AbstractJdbc3gConnection.<init>(AbstractJdbc3gConnection.java:20)
at org.postgresql.jdbc4.AbstractJdbc4Connection.<init>(AbstractJdbc4Connection.java:30)
at org.postgresql.jdbc4.Jdbc4Connection.<init>(Jdbc4Connection.java:22)
at org.postgresql.Driver.makeConnection(Driver.java:391)
at org.postgresql.Driver.connect(Driver.java:265)
at play.utils.ProxyDriver.connect(ProxyDriver.scala:9)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at com.jolbox.bonecp.BoneCP.obtainRawInternalConnection(BoneCP.java:256)
at com.jolbox.bonecp.BoneCP.<init>(BoneCP.java:305)
at com.jolbox.bonecp.BoneCPDataSource.maybeInit(BoneCPDataSource.java:150)
at com.jolbox.bonecp.BoneCPDataSource.getConnection(BoneCPDataSource.java:112)
at play.api.db.DBApi$class.getConnection(DB.scala:64)
at play.api.db.BoneCPApi.getConnection(DB.scala:273)
at play.api.db.evolutions.Evolutions$.databaseEvolutions(Evolutions.scala:306)
at play.api.db.evolutions.Evolutions$.evolutionScript(Evolutions.scala:284)
at play.api.db.evolutions.OfflineEvolutions$.applyScript(Evolutions.scala:452)
at play.core.ReloadableApplication.handleWebCommand(ApplicationProvider.scala:175)
at play.core.server.Server$$anonfun$getHandlerFor$1.apply(Server.scala:86)
at play.core.server.Server$$anonfun$getHandlerFor$1.apply(Server.scala:86)
at scala.util.control.Exception$Catch$$anonfun$either$1.apply(Exception.scala:110)
at scala.util.control.Exception$Catch$$anonfun$either$1.apply(Exception.scala:110)
at scala.util.control.Exception$Catch.apply(Exception.scala:88)
at scala.util.control.Exception$Catch.either(Exception.scala:110)
at play.core.server.Server$class.getHandlerFor(Server.scala:86)
at play.core.server.NettyServer.getHandlerFor(NettyServer.scala:38)
at play.core.server.netty.PlayDefaultUpstreamHandler.messageReceived(PlayDefaultUpstreamHandler.scala:226)
at org.jboss.netty.channel.SimpleChannelUpstreamHandler.handleUpstream(SimpleChannelUpstreamHandler.java:75)
at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:558)
at org.jboss.netty.channel.DefaultChannelPipeline$DefaultChannelHandlerContext.sendUpstream(DefaultChannelPipeline.java:777)
at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:296)
at org.jboss.netty.handler.codec.replay.ReplayingDecoder.unfoldAndFireMessageReceived(ReplayingDecoder.java:522)
at org.jboss.netty.handler.codec.replay.ReplayingDecoder.callDecode(ReplayingDecoder.java:501)
at org.jboss.netty.handler.codec.replay.ReplayingDecoder.messageReceived(ReplayingDecoder.java:438)
at org.jboss.netty.channel.SimpleChannelUpstreamHandler.handleUpstream(SimpleChannelUpstreamHandler.java:75)
at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:558)
at org.jboss.netty.channel.DefaultChannelPipeline.sendUpstream(DefaultChannelPipeline.java:553)
at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:268)
at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:255)
at org.jboss.netty.channel.socket.nio.NioWorker.read(NioWorker.java:343)
at org.jboss.netty.channel.socket.nio.NioWorker.processSelectedKeys(NioWorker.java:274)
at org.jboss.netty.channel.socket.nio.NioWorker.run(NioWorker.java:194)
at org.jboss.netty.util.ThreadRenamingRunnable.run(ThreadRenamingRunnable.java:102)
at org.jboss.netty.util.internal.DeadLockProofWorker$1.run(DeadLockProofWorker.java:42)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
开发数据库具有固定数量的可用连接（大约 20 个）。如何确保正确关闭连接？