【发布时间】：2012-12-30 18:05:48
【问题描述】：
我正在使用 c3p0 连接池在我的（未签名的）Java 小程序和 MySql 数据库之间进行通信。 我有这个初始化池的代码：
DataSource pool = pools.get(db_name);
if(pool == null)
pool = initializePool(db_name);
return pool.getConnection();
初始化池方法如下：
protected DataSource initializePool(String db_name) throws SQLException {
try {
ComboPooledDataSource cpds = new ComboPooledDataSource();
cpds.setDriverClass("com.mysql.jdbc.Driver");
cpds.setJdbcUrl(connectionDetails.getConnectionString(db_name));
cpds.setUser(connectionDetails.getUsername());
cpds.setPassword(connectionDetails.getPassword());
pools.put(db_name, cpds);
return cpds;
} catch (PropertyVetoException e) {
e.printStackTrace();
throw new SQLException("JDBC driver could not be initialized propertly");
}
}
我的 c3p0-config.xml 很简单：
<c3p0-config><default-config>
<property name="acquireIncrement">1</property>
<property name="initialPoolSize">5</property>
<property name="minPoolSize">1</property>
<property name="maxPoolSize">7</property>
<property name="maxConnectionAge">0</property>
<property name="maxIdleTime">600</property>
<property name="maxIdleTimeExcessConnections">120</property>
<property name="automaticTestTable">C3p0_test_table</property>
<property name="idleConnectionTestPeriod">60</property>
<property name="testConnectionOnCheckin">true</property></default-config></c3p0-config>
问题是，当我第一次调用数据库时，“getConnection”调用有时甚至需要 10 秒或更长时间才能响应（第二次我联系数据库时它更快）。我一直在寻找整个网络和“c3p0”手册以寻找加速连接池的方法，但没有运气。
当我（从服务器）运行我的小程序时，java 控制台输出如下所示：
Jan 16, 2013 12:57:14 PM com.mchange.v2.log.MLog <clinit>
INFO: MLog clients using java 1.4+ standard logging.
Jan 16, 2013 12:57:16 PM com.mchange.v2.c3p0.C3P0Registry <clinit>
INFO: jdk1.5 management interfaces unavailable... JMX support disabled.
java.security.AccessControlException: access denied ("javax.management.MBeanServerPermission" "createMBeanServer")
at java.security.AccessControlContext.checkPermission(Unknown Source)
at java.security.AccessController.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkPermission(Unknown Source)
at java.lang.management.ManagementFactory.getPlatformMBeanServer(Unknown Source)
at com.mchange.v2.c3p0.management.ActiveManagementCoordinator.<init>(ActiveManagementCoordinator.java:42)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at java.lang.Class.newInstance0(Unknown Source)
at java.lang.Class.newInstance(Unknown Source)
at com.mchange.v2.c3p0.C3P0Registry.<clinit>(C3P0Registry.java:134)
at com.mchange.v2.c3p0.impl.PoolBackedDataSourceBase.<init>(PoolBackedDataSourceBase.java:228)
at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.<init>(AbstractPoolBackedDataSource.java:62)
at com.mchange.v2.c3p0.ComboPooledDataSource.<init>(ComboPooledDataSource.java:109)
at com.mchange.v2.c3p0.ComboPooledDataSource.<init>(ComboPooledDataSource.java:105)
...
Jan 16, 2013 12:57:16 PM com.mchange.v2.c3p0.C3P0Registry banner
INFO: Initializing c3p0-0.9.1.2 [built 21-May-2007 15:05:05; debug? true; trace: 10]
Jan 16, 2013 12:57:16 PM com.mchange.v2.c3p0.PoolConfig <clinit>
WARNING: Read of system Properties blocked -- ignoring any c3p0 configuration via System properties! (But any configuration via a c3p0.properties file is still okay!)
java.security.AccessControlException: access denied ("java.util.PropertyPermission" "*" "read,write")
at java.security.AccessControlContext.checkPermission(Unknown Source)
at java.security.AccessController.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkPropertiesAccess(Unknown Source)
at java.lang.System.getProperties(Unknown Source)
at com.mchange.v2.c3p0.PoolConfig.<clinit>(PoolConfig.java:101)
at com.mchange.v2.c3p0.impl.C3P0ImplUtils.defaultConnectionTester(C3P0ImplUtils.java:283)
at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.<init>(WrapperConnectionPoolDataSource.java:47)
at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.<init>(WrapperConnectionPoolDataSource.java:67)
at com.mchange.v2.c3p0.ComboPooledDataSource.<init>(ComboPooledDataSource.java:114)
at com.mchange.v2.c3p0.ComboPooledDataSource.<init>(ComboPooledDataSource.java:105)
...
started taking connection - Wed Jan 16 12:57:16 CET 2013
Jan 16, 2013 12:57:20 PM com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource getPoolManager
INFO: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ some connection info and params for DB1]
Connection taken - Wed Jan 16 12:57:23 CET 2013
started taking connection - Wed Jan 16 12:57:23 CET 2013
Jan 16, 2013 12:57:24 PM com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource getPoolManager
INFO: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ some connection info and params for DB2]
Connection taken - Wed Jan 16 12:57:24 CET 2013
我错过了什么？有没有办法加快获得连接的过程？我认为这可能是服务器问题，但即使我从 Eclipse 运行我的小程序（并使其与服务器上的远程数据库联系），我也会遇到这些滞后。请帮忙，或者至少解释一下为什么连接这么慢？
【问题讨论】：
-
使用其他工具（如mysql命令行客户端）连接远程数据库需要多长时间？您确定这不仅仅是网络延迟，还是 DNS 解析花费的时间太长？每次启动小程序时都会出现相同的延迟，还是退出小程序并重新启动它会更快？
-
嗯，当我从 localhost 启动它并连接到远程数据库时它会更快。奇怪的问题是当 applet 和 db 都在服务器上并且我正在从我的计算机上测试 applet 时。当我关闭小程序并重新启动它时，它运行得更快，但不多。命令行mysql速度很快。