如何为c3p0设置getConnection()超时？

Question

昨天AWS的RDS下降了 - 我们的数据库也是如此.

发生这种情况时,C3P0会尝试获取数据库连接并挂起.我显然希望我的应用程序在这些实例中返回错误页面,而不是仅仅等待响应.

这是代码的样子:

ComboPooledDataSource db = new ComboPooledDataSource();
...
Connection conn = db.getConnection();

如何设置从c3p0的连接池获取连接的超时？

我以为checkoutTimeout()就是它 - 但事实并非如此.它是"当池耗尽时,客户端调用getConnection()将等待连接被签入或获取的毫秒数." 由于池没有用尽(它只是不可用),这不适用.

我还认为setAcquireRetryAttempts和setAcquireIncrement可以工作 - 但是它们不会因为连接没有失败,所以它只是没有响应.

当我拉动整个堆栈时,这就是它停止的地方:

SocketInputStream.socketRead0(FileDescriptor, byte[], int, int, int) line: not available [native method]    
SocketInputStream.read(byte[], int, int) line: 129  
ReadAheadInputStream.fill(int) line: 113    
ReadAheadInputStream.readFromUnderlyingStreamIfNecessary(byte[], int, int) line: 160    
ReadAheadInputStream.read(byte[], int, int) line: 188   
MysqlIO.readFully(InputStream, byte[], int, int) line: 2428 
MysqlIO.reuseAndReadPacket(Buffer, int) line: 2882  
MysqlIO.reuseAndReadPacket(Buffer) line: 2871   
MysqlIO.checkErrorPacket(int) line: 3414    
MysqlIO.sendCommand(int, String, Buffer, boolean, String) line: 1936    
MysqlIO.sqlQueryDirect(StatementImpl, String, String, Buffer, int, int, int, boolean, String, Field[]) line: 2060   
JDBC4Connection(ConnectionImpl).execSQL(StatementImpl, String, int, Buffer, int, int, boolean, String, Field[], boolean) line: 2542 
JDBC4PreparedStatement(PreparedStatement).executeInternal(int, Buffer, boolean, boolean, Field[], boolean) line: 1734   
JDBC4PreparedStatement(PreparedStatement).executeQuery() line: 1885 
NewProxyPreparedStatement.executeQuery() line: 76   
C3P0PooledConnectionPoolManager.initializeAutomaticTestTable(String, DbAuth) line: 799  
C3P0PooledConnectionPoolManager.createPooledConnectionPool(DbAuth) line: 696    
C3P0PooledConnectionPoolManager.getPool(DbAuth) line: 257   
C3P0PooledConnectionPoolManager.getPool() line: 271 
ComboPooledDataSource(AbstractPoolBackedDataSource).getNumThreadsAwaitingCheckoutDefaultUser() line: 203    
NativeMethodAccessorImpl.invoke0(Method, Object, Object[]) line: not available [native method]  
NativeMethodAccessorImpl.invoke(Object, Object[]) line: 39  
DelegatingMethodAccessorImpl.invoke(Object, Object[]) line: 25  
Method.invoke(Object, Object...) line: 597  
BeansUtils.extractAccessiblePropertiesToMap(Map, Object, Collection) line: 359  
BeansUtils.appendPropNamesAndValues(StringBuffer, Object, Collection) line: 324 
ComboPooledDataSource.toString() line: 539  
ComboPooledDataSource(AbstractPoolBackedDataSource).getPoolManager() line: 462  
ComboPooledDataSource(AbstractPoolBackedDataSource).getConnection() line: 128   

当我搜索"socketRead0 timeout"和"socketRead0 hang"时 - 我看到很多问题,但没有真正的解决方案.

有没有办法在这里强制超时？

谢谢!

Answer 1

问题出在 MySQL 的 ReadAheadInputStream 中，它使用阻塞读取。本机套接字被阻止并且从不（？）返回错误代码。所以连接也挂起。

除了将代码放入线程中并在超时的情况下 join() 到它之外，我没有找到处理它的方法。我不认为这个问题可以证明复杂性是合理的：我希望亚马逊能够从停机中得出正确的结论，并且不会让这种情况再次发生。