org.springframework.transaction.CannotCreateTransactionException: Could not open JDBC Connection for transaction; nested exception is java.sql.SQLTransientConnectionException: Connection is not available, request timed out after 60059ms.
at org.springframework.jdbc.datasource.DataSourceTransactionManager.doBegin(DataSourceTransactionManager.java:305) ~[spring-jdbc-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:378) ~[spring-tx-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
at org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:474) ~[spring-tx-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:289) ~[spring-tx-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:98) ~[spring-tx-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92) ~[spring-aop-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185) ~[spring-aop-5.0.5.RELEASE.jar!/:5.0.5.RELEASE]
1.系统在低峰的时候访问快，高峰的时候访问慢，有时候还会报错。从打印出SQL的执行时间上看，同样的SQL有时候10ms，有时候6s，差异非常大。
2.通过分析数据库慢日志，发现执行都很快，且数据库并没有出现性能瓶颈。
3.判断是tomcat数据库连接池太小，检查果然，最大只有10。
4.覆盘，SQL执行时快时慢是因为获取不到连接在等待，严重的时候会等待超时。