我们的项目中有Spring-boot / Hibernate /
PostgreSQL应用程序，并使用Hikari作为连接池。我们一直遇到以下问题：几个小时后，活动的连接数增长到了极限，并且出现了这样的错误（完整的堆栈跟踪位于问题的结尾）：

Caused by: java.sql.SQLTransientConnectionException: HikariPool-0 - Connection is not available, request timed out after 30000ms.
    at com.zaxxer.hikari.pool.HikariPool.getConnection(HikariPool.java:213) ~[HikariCP-2.4.1.jar:na]
    at com.zaxxer.hikari.pool.HikariPool.getConnection(HikariPool.java:163) ~[HikariCP-2.4.1.jar:na]
    at com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:85) ~[HikariCP-2.4.1.jar:na]
    at org.hibernate.engine.jdbc.connections.internal.DatasourceConnectionProviderImpl.getConnection(DatasourceConnectionProviderImpl.java:139) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.internal.AbstractSessionImpl$NonContextualJdbcConnectionAccess.obtainConnection(AbstractSessionImpl.java:380) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:228) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    ... 126 common frames omitted

这是版本信息：

Spring-boot version:   1.2.3.RELEASE
HikariCP version:      2.4.1
Hibernate version:     4.3.6.Final
Postgresql jdbc:       9.3-1102-jdbc41
Server version:        Apache Tomcat/8.0.23
JVM Version:           1.8.0_45-b14

JPA /hibernate配置：

jpa:
    database-platform: org.hibernate.dialect.PostgreSQL82Dialect
    database: POSTGRESQL
    openInView: false
    show_sql: false
    generate-ddl: false
    hibernate:
        ddl-auto: none
        naming-strategy: org.hibernate.cfg.EJB3NamingStrategy
    properties:
        hibernate.cache.use_second_level_cache: true
        hibernate.cache.use_query_cache: false
        hibernate.generate_statistics: false
        hibernate.cache.region.factory_class: org.hibernate.cache.ehcache.SingletonEhCacheRegionFactory
        hibernate.enable_lazy_load_no_trans: true
        hibernate.event.merge.entity_copy_observer: allow

HikariCP配置：

2015-10-06 12:26:44,252 DEBUG [localhost-startStop-1] HikariConfig: HikariPool-0 - configuration:
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: allowPoolSuspension.............false
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: autoCommit......................true
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: catalog.........................
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: connectionInitSql...............
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: connectionTestQuery.............
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: connectionTimeout...............30000
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: dataSource......................
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: dataSourceClassName.............org.postgresql.ds.PGSimpleDataSource
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: dataSourceJNDI..................
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: dataSourceProperties............{user=postgres, password=<masked>, databaseName=lms, serverName=*.*.*.*:5432}
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: driverClassName.................
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: healthCheckProperties...........{}
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: healthCheckRegistry.............
2015-10-06 12:26:44,274 DEBUG [localhost-startStop-1] HikariConfig: idleTimeout.....................30000
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: initializationFailFast..........true
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: isolateInternalQueries..........false
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: jdbc4ConnectionTest.............false
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: jdbcUrl.........................
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: leakDetectionThreshold..........0
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: maxLifetime.....................1800000
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: maximumPoolSize.................20
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: metricRegistry..................com.codahale.metrics.MetricRegistry@63d2fc48
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: metricsTrackerFactory...........
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: minimumIdle.....................10
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: password........................<masked>
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: poolName........................HikariPool-0
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: readOnly........................false
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: registerMbeans..................false
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: scheduledExecutorService........
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: threadFactory...................
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: transactionIsolation............
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: username........................
2015-10-06 12:26:44,275 DEBUG [localhost-startStop-1] HikariConfig: validationTimeout...............5000
2015-10-06 12:26:44,276 INFO  [localhost-startStop-1] HikariDataSource: HikariPool-0 - is starting.
2015-10-06 12:26:44,432 DEBUG [localhost-startStop-1] PoolElf: HikariPool-0 - Connection.setNetworkTimeout() is not supported (Method org.postgresql.jdbc4.Jdbc4Connection.getNetworkTimeout() is not yet implemented.)

完整堆栈跟踪：

2015-10-06 12:09:36,885 DEBUG [http-nio-8080-exec-25] PoolElf: HikariPool-0 - Reset (nothing) on connection org.postgresql.jdbc4.Jdbc4Connection@3cc4d919
2015-10-06 12:09:42,651 DEBUG [Hikari housekeeper (pool HikariPool-0)] HikariPool: Before cleanup   pool HikariPool-0 stats (total=20, active=20, idle=0, waiting=1)
2015-10-06 12:09:42,652 DEBUG [Hikari housekeeper (pool HikariPool-0)] HikariPool: After cleanup    pool HikariPool-0 stats (total=20, active=20, idle=0, waiting=1)
2015-10-06 12:10:06,885 DEBUG [http-nio-8080-exec-25] HikariPool: Timeout failure   pool HikariPool-0 stats (total=20, active=20, idle=0, waiting=0)
2015-10-06 12:10:06,885 WARN  [http-nio-8080-exec-25] SqlExceptionHelper: SQL Error: 0, SQLState: null
2015-10-06 12:10:06,885 ERROR [http-nio-8080-exec-25] SqlExceptionHelper: HikariPool-0 - Connection is not available, request timed out after 30000ms.
2015-10-06 12:10:06,885 DEBUG [http-nio-8080-exec-25] PoolElf: HikariPool-0 - Reset (nothing) on connection org.postgresql.jdbc4.Jdbc4Connection@3cc4d919
2015-10-06 12:10:06,886 ERROR [http-nio-8080-exec-25] ErrorPageFilter: Forwarding to error page from request [/api/courses/121387/quizzes/i6fa2562510bf8578712380a87a433e97/student/30175] due to exception [org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.hibernate.exception.JDBCConnectionException: Could not open connection]
java.lang.RuntimeException: org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.hibernate.exception.JDBCConnectionException: Could not open connection
    at lms.security.xauth.XAuthTokenFilter.doFilter(XAuthTokenFilter.java:86) ~[XAuthTokenFilter.class:na]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:120) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:64) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:91) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:53) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:213) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:176) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [catalina.jar:8.0.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.23]
    at org.springframework.boot.actuate.trace.WebRequestTraceFilter.doFilterInternal(WebRequestTraceFilter.java:102) ~[spring-boot-actuator-1.2.3.RELEASE.jar:1.2.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [catalina.jar:8.0.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.23]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:85) ~[spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [catalina.jar:8.0.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.23]
    at org.springframework.boot.context.web.ErrorPageFilter.doFilter(ErrorPageFilter.java:113) [spring-boot-1.2.3.RELEASE.jar:1.2.3.RELEASE]
    at org.springframework.boot.context.web.ErrorPageFilter.access$000(ErrorPageFilter.java:59) [spring-boot-1.2.3.RELEASE.jar:1.2.3.RELEASE]
    at org.springframework.boot.context.web.ErrorPageFilter$1.doFilterInternal(ErrorPageFilter.java:88) [spring-boot-1.2.3.RELEASE.jar:1.2.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.boot.context.web.ErrorPageFilter.doFilter(ErrorPageFilter.java:106) [spring-boot-1.2.3.RELEASE.jar:1.2.3.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [catalina.jar:8.0.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.23]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219) [catalina.jar:8.0.23]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) [catalina.jar:8.0.23]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502) [catalina.jar:8.0.23]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142) [catalina.jar:8.0.23]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [catalina.jar:8.0.23]
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:617) [catalina.jar:8.0.23]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) [catalina.jar:8.0.23]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518) [catalina.jar:8.0.23]
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091) [tomcat-coyote.jar:8.0.23]
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668) [tomcat-coyote.jar:8.0.23]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1521) [tomcat-coyote.jar:8.0.23]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1478) [tomcat-coyote.jar:8.0.23]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_45]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_45]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-util.jar:8.0.23]
    at java.lang.Thread.run(Thread.java:745) [na:1.8.0_45]
Caused by: org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.hibernate.exception.JDBCConnectionException: Could not open connection
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:978) ~[spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:868) ~[spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:648) ~[servlet-api.jar:na]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842) ~[spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) ~[servlet-api.jar:na]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291) [catalina.jar:8.0.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.23]
    at com.codahale.metrics.servlet.AbstractInstrumentedFilter.doFilter(AbstractInstrumentedFilter.java:104) ~[metrics-servlet-3.1.1.jar:3.1.1]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [catalina.jar:8.0.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.23]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-websocket.jar:8.0.23]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [catalina.jar:8.0.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.23]
    at org.springframework.boot.actuate.autoconfigure.EndpointWebMvcAutoConfiguration$ApplicationContextHeaderFilter.doFilterInternal(EndpointWebMvcAutoConfiguration.java:291) ~[spring-boot-actuator-1.2.3.RELEASE.jar:1.2.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [catalina.jar:8.0.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.23]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77) ~[spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) [spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) [catalina.jar:8.0.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) [catalina.jar:8.0.23]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:316) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:126) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:90) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:114) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:122) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:111) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:168) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:48) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330) ~[spring-security-web-4.0.0.RELEASE.jar:na]
    at lms.security.xauth.XAuthTokenFilter.doFilter(XAuthTokenFilter.java:84) ~[XAuthTokenFilter.class:na]
    ... 46 common frames omitted
Caused by: org.hibernate.exception.JDBCConnectionException: Could not open connection
    at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:65) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:126) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:112) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:235) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.getConnection(LogicalConnectionImpl.java:171) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.doBegin(JdbcTransaction.java:67) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.begin(AbstractTransactionImpl.java:162) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.internal.SessionImpl.beginTransaction(SessionImpl.java:1435) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:250) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.collection.internal.AbstractPersistentCollection.readElementByIndex(AbstractPersistentCollection.java:376) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.collection.internal.PersistentMap.get(PersistentMap.java:164) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at java_util_Map$get.call(Unknown Source) ~[na:na]
    at lms.service.QuizService.processAnswers(QuizService.groovy:66) ~[QuizService.class:na]
    at lms.service.QuizService$$FastClassBySpringCGLIB$$4dcc8beb.invoke(<generated>) ~[spring-core-4.1.6.RELEASE.jar:na]
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204) ~[spring-core-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:717) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99) ~[spring-tx-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:281) ~[spring-tx-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96) ~[spring-tx-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:653) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at lms.service.QuizService$$EnhancerBySpringCGLIB$$37a60c0a.processAnswers(<generated>) ~[spring-core-4.1.6.RELEASE.jar:na]
    at lms.web.rest.CourseResource.saveQuizResults(CourseResource.java:537) ~[CourseResource.class:na]
    at lms.web.rest.CourseResource$$FastClassBySpringCGLIB$$e3d2ba4d.invoke(<generated>) ~[spring-core-4.1.6.RELEASE.jar:na]
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204) ~[spring-core-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:717) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.security.access.intercept.aopalliance.MethodSecurityInterceptor.invoke(MethodSecurityInterceptor.java:68) ~[spring-security-core-4.0.0.RELEASE.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at com.ryantenney.metrics.spring.TimedMethodInterceptor.invoke(TimedMethodInterceptor.java:48) ~[metrics-spring-3.0.4.jar:na]
    at com.ryantenney.metrics.spring.TimedMethodInterceptor.invoke(TimedMethodInterceptor.java:34) ~[metrics-spring-3.0.4.jar:na]
    at com.ryantenney.metrics.spring.AbstractMetricMethodInterceptor.invoke(AbstractMetricMethodInterceptor.java:59) ~[metrics-spring-3.0.4.jar:na]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:653) ~[spring-aop-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at lms.web.rest.CourseResource$$EnhancerBySpringCGLIB$$ff854301.saveQuizResults(<generated>) ~[spring-core-4.1.6.RELEASE.jar:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_45]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_45]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_45]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_45]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221) ~[spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:137) ~[spring-web-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110) ~[spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:776) ~[spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:705) ~[spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959) ~[spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893) ~[spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966) ~[spring-webmvc-4.1.6.RELEASE.jar:4.1.6.RELEASE]
    ... 81 common frames omitted
Caused by: java.sql.SQLTransientConnectionException: HikariPool-0 - Connection is not available, request timed out after 30000ms.
    at com.zaxxer.hikari.pool.HikariPool.getConnection(HikariPool.java:213) ~[HikariCP-2.4.1.jar:na]
    at com.zaxxer.hikari.pool.HikariPool.getConnection(HikariPool.java:163) ~[HikariCP-2.4.1.jar:na]
    at com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:85) ~[HikariCP-2.4.1.jar:na]
    at org.hibernate.engine.jdbc.connections.internal.DatasourceConnectionProviderImpl.getConnection(DatasourceConnectionProviderImpl.java:139) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.internal.AbstractSessionImpl$NonContextualJdbcConnectionAccess.obtainConnection(AbstractSessionImpl.java:380) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:228) ~[hibernate-core-4.3.6.Final.jar:4.3.6.Final]
    ... 126 common frames omitted
2015-10-06 12:10:12,651 DEBUG [Hikari housekeeper (pool HikariPool-0)] HikariPool: Before cleanup   pool HikariPool-0 stats (total=20, active=19, idle=1, waiting=0)
2015-10-06 12:10:12,652 DEBUG [Hikari housekeeper (pool HikariPool-0)] HikariPool: After cleanup    pool HikariPool-0 stats (total=20, active=19, idle=1, waiting=0)

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