java.lang.Exception: Apparent connection leak detected

16-05-2019 13:25:46.494 [HikariPool-1 housekeeper] WARN  com.zaxxer.hikari.pool.ProxyLeakTask.run - Connection leak detection triggered for com.mysql.jdbc.JDBC4Connection@7c3beffb, stack trace follows
java.lang.Exception: Apparent connection leak detected
    at org.springframework.jdbc.datasource.DataSourceUtils.doGetConnection(DataSourceUtils.java:111)
    at org.springframework.jdbc.datasource.DataSourceUtils.getConnection(DataSourceUtils.java:77)
    at org.mybatis.spring.transaction.SpringManagedTransaction.openConnection(SpringManagedTransaction.java:84)
    at org.mybatis.spring.transaction.SpringManagedTransaction.getConnection(SpringManagedTransaction.java:70)
    at org.apache.ibatis.executor.BaseExecutor.getConnection(BaseExecutor.java:336)
    at org.apache.ibatis.executor.SimpleExecutor.prepareStatement(SimpleExecutor.java:84)
    at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:62)
    at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:324)
    at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:156)
    at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:109)
    at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:83)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:148)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:141)
    at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:77)
    at sun.reflect.GeneratedMethodAccessor148.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:434)
    at com.sun.proxy.$Proxy107.selectOne(Unknown Source)
    at org.mybatis.spring.SqlSessionTemplate.selectOne(SqlSessionTemplate.java:167)
 

# hikari 连接池配置如下
spring.datasource.username=root
spring.datasource.password=root
spring.datasource.hikari.idle-timeout=3000
spring.datasource.hikari.max-lifetime=6000
spring.datasource.hikari.minimum-idle=10
spring.datasource.hikari.maximum-pool-size=100
spring.datasource.hikari.leak-detection-threshold=5000

leak-detection-threshold:用来设置连接被占用的超时时间，单位为毫秒，默认为0，表示禁用连接泄露检测。
connection-timeout:从连接池获取连接的超时时间。

分析源代码发现，该错误的原因是从连接池获取连接超时，触发了连接泄露检测。此处spring调用了doGetConnection从hikari中获取连接
在org.springframework.jdbc.datasource.DataSourceUtils#doGetConnection中，

也就是说，获取到连接之后使用之前的时间+使用连接的时间+使用之后还回连接之前的时间，超出了leakDetectionThreshold毫秒，就抛出检测到连接泄露的异常。结合我们的业务发现，此处确实是使用连接的时间超出了leakDetectionThreshold毫秒，是因为执行了慢 sql，同时慢 sql 耗尽了连接池的连接，导致新线程获取连接超时，又导致了获取连接超时的报错。
# 这个调大即可
spring.datasource.hikari.leak-detection-threshold=50000