问题现象

日志出现如下关键信息：

Caused by: org.hibernate.exception.JDBCConnectionException: Unable to acquire JDBC Connection
at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:48)
at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42)
at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:113)
at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:99)
at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.acquireConnectionIfNeeded(LogicalConnectionManagedImpl.java:109)
at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.getPhysicalConnection(LogicalConnectionManagedImpl.java:136)
at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.getConnectionForTransactionManagement(LogicalConnectionManagedImpl.java:254)
at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.begin(LogicalConnectionManagedImpl.java:262)
at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl$TransactionDriverControlImpl.begin(JdbcResourceLocalTransactionCoordinatorImpl.java:236)
at org.hibernate.engine.transaction.internal.TransactionImpl.begin(TransactionImpl.java:86)
at org.springframework.orm.jpa.vendor.HibernateJpaDialect.beginTransaction(HibernateJpaDialect.java:184)
at org.springframework.orm.jpa.JpaTransactionManager.doBegin(JpaTransactionManager.java:402)
… 38 common frames omitted
Caused by: java.sql.SQLTransientConnectionException: Hikari - Connection is not available, request timed out after 30000ms.
at com.zaxxer.hikari.pool.HikariPool.createTimeoutException(HikariPool.java:695)
at com.zaxxer.hikari.pool.HikariPool.getConnection(HikariPool.java:197)
at com.zaxxer.hikari.pool.HikariPool.getConnection(HikariPool.java:162)
at com.zaxxer.hikari.HikariDataSource.getConnection(HikariDataSource.java:128)
at org.hibernate.engine.jdbc.connections.internal.DatasourceConnectionProviderImpl.getConnection(DatasourceConnectionProviderImpl.java:122)
at org.hibernate.internal.NonContextualJdbcConnectionAccess.obtainConnection(NonContextualJdbcConnectionAccess.java:35)
at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.acquireConnectionIfNeeded(LogicalConnectionManagedImpl.java:106)
… 45 common frames omitted

如果配置了相关监控，
很有可能会发现激活连接数（Hikari.pool.ActiveConnections）等于或者接近于最大连接数（Hikari.pool.MaxConnections）

问题分析

根据以上信息，基本可以确定是由于数据库连接池中活跃连接太多，无法获取新的连接，超过了了指定的超时时间后报错。

如果你的系统访问并发并不大，使用jstack命令打印线程信息发现也没有线程处于数据库操作的状态，则很有可能是某一处代码获取连接后没有及时释放导致。

那么如何定位是哪里的代码导致的呢？

可以使用hikari提供的泄漏检测功能，配置如下参数：

spring.datasource.hikari.leak-detection-threshold=10000

添加该参数后，如果某个线程没有释放连接，在获取连接 10000 毫秒后，系统会以WARN级别打印线程堆栈，而且不影响主程序运行。可以准确判断是哪一处代码引起，如下所示：

该配置会有一定的性能损耗，问题排查解决后建议关闭配置

参考

聊聊hikari连接池的leakDetectionThreshold

What constitutes an “Active” connnection? #862