https://my.oschina.net/haogrgr/blog/224010

今天在一台配置很低的机器上运行批量更新的程序~~~

大概跑了三十分钟~~~这配置~~~这程序~~~

然后华丽丽的报异常了~~~

具体异常是这样的,

DEBUG: (BaseJdbcLogger.java:132)    ooo Using Connection [com.alibaba.druid.proxy.jdbc.ConnectionProxyImpl@4d4e22e1] [2014-07-17 15:19:35]5363945354 [Druid-ConnectionPool-Destory-1422598563] com.alibaba.druid.pool.DruidDataSource:1132  WARN : (DruidDataSource.java:1132)   get/close not same thread ERROR: (DruidDataSource.java:1815)   abandon connection, open stackTrace         at java.lang.Thread.getStackTrace(Thread.java:1588) at com.alibaba.druid.pool.DruidDataSource.getConnectionDirect(DruidDataSource.java:942) at com.alibaba.druid.filter.FilterChainImpl.dataSource_connect(FilterChainImpl.java:4534) at com.alibaba.druid.filter.stat.StatFilter.dataSource_getConnection(StatFilter.java:661) at com.alibaba.druid.filter.FilterChainImpl.dataSource_connect(FilterChainImpl.java:4530) at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:880) at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:872) at com.alibaba.druid.pool.DruidDataSource.getConnection(DruidDataSource.java:97)

这个是最初的异常, 后面还有一大批异常,

Caused by: java.sql.SQLException: connection holder is null at com.alibaba.druid.pool.DruidPooledConnection.checkState(DruidPooledConnection.java:1085) at com.alibaba.druid.pool.DruidPooledConnection.getMetaData(DruidPooledConnection.java:825) at org.springframework.jdbc.support.JdbcUtils.extractDatabaseMetaData(JdbcUtils.java:285) ... 70 more

说什么holder为空

第一眼看到holder就像到Spring的源码, 里面到处是holder(笑)

但是这里的holder不是Spirng里面的,是Druid的

这个holder大概是用来hou住连接池里面的连接的.

然后为什么为空了呢? 目测是哪个链接坏了, 或者被意外的关闭了...

根据异常调源码  at com.alibaba.druid.pool.DruidDataSource.getConnectionDirect(DruidDataSource.java:942)

941         if (isRemoveAbandoned()) {
942                StackTraceElement[] stackTrace = Thread.currentThread().getStackTrace();
943                poolalbeConnection.setConnectStackTrace(stackTrace);                 poolalbeConnection.setConnectedTimeNano();                 poolalbeConnection.setTraceEnable(true);                 synchronized (activeConnections) {                     activeConnections.put(poolalbeConnection, PRESENT);                 }             }

看不出啥来. 只能将日志继续看看, 还是看不出啥来

然后看了上面代码几遍后, 老觉得 isRemoveAbandoned() 这个方法有鬼.

查看调用处,:

恩, 这个DestroyConnectionThread非常可疑, 跳

                    if (isRemoveAbandoned()) {removeAbandoned();}

继续

    public int removeAbandoned() {         int removeCount = 0;         long currrentNanos = System.nanoTime();         List<DruidPooledConnection> abandonedList = new ArrayList<DruidPooledConnection>();         synchronized (activeConnections) {             Iterator<DruidPooledConnection> iter = activeConnections.keySet().iterator();             for (; iter.hasNext();) {                 DruidPooledConnection pooledConnection = iter.next();                 if (pooledConnection.isRunning()) {                     continue;                 }                 long timeMillis = (currrentNanos - pooledConnection.getConnectedTimeNano()) / (1000 * 1000);                 if (timeMillis >= removeAbandonedTimeoutMillis) {                     iter.remove();                     pooledConnection.setTraceEnable(false);                     abandonedList.add(pooledConnection);                 }             }         } ....略     }

擦, 这里不对头,   timeMillis >= removeAbandonedTimeoutMillis  timeMillis 这个是getConnection()被调用时的时间

意思就是一个连接被get后, 超过了 removeAbandonedTimeoutMillis这么久我就弄死你.

然后继续找removeAbandonedTimeoutMillis 这玩意在哪里设置的   ,最后发现是在

<property name="removeAbandoned" value="true" />

<property name="removeAbandonedTimeout" value="1800" />

初始化配置的这里设置的,  这两个参数的大概意思就是,

通过datasource.getConnontion() 取得的连接必须在removeAbandonedTimeout这么多秒内调用close(),要不我就弄死你.(就是conn不能超过指定的租期)

然后调成2个小时~~~

然后程序成功跑完~~~华丽丽的等了50分钟

总结:

连接池为了防止程序从池里取得连接后忘记归还的情况, 而提供了一些参数来设置一个租期, 使用这个可以在一定程度上防止连接泄漏

但是如果你的业务真要跑这么久~~~~那还是注意下这个设置.