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本文主要介绍下jdbc的socket timeout的设置

jdbc timeout类别

主要有如下几个类别

transaction timeout

设置的是一个事务的执行时间，里头可能包含多个statement

statement timeout(也相当于result set fetch timeout)

设置的是一个statement的执行超时时间，即driver等待statement执行完成，接收到数据的超时时间(注意statement的timeout不是整个查询的timeout，只是statement执行完成并拉取fetchSize数据返回的超时，之后resultSet的next在必要的时候还会触发fetch数据，每次fetch的超时时间是单独算的，默认也是以statement设置的timeout为准)

jdbc socket timeout

设置的是jdbc I/O socket read and write operations的超时时间，防止因网络问题或数据库问题，导致driver一直阻塞等待。(建议比statement timeout的时间长)

os socket timeout

这个是操作系统级别的socket设置(如果jdbc socket timeout没有设置，而os级别的socket timeout有设置，则使用系统的socket timeout值)。

上面的不同级别的timeout越往下优先级越高，也就是说如果下面的配置比上面的配置值小的话，则会优先触发timeout，那么相当于上面的配置值就"失效"了。

jdbc socket timeout

这个不同数据的jdbc driver实现不一样

mysql

jdbc:mysql://localhost:3306/ag_admin?useUnicode=true&amp;characterEncoding=UTF8&connectTimeout=60000&socketTimeout=60000

通过url参数传递即可

pg

jdbc:postgresql://localhost/test?user=fred&password=secret&&connectTimeout=60&socketTimeout=60

pg也是通过url传递，不过它的单位与mysql不同，mysql是毫秒，而pg是秒

oracle

oracle需要通过oracle.jdbc.ReadTimeout参数来设置，连接超时参数是oracle.net.CONNECT_TIMEOUT

通过properties设置

            Class.forName("oracle.jdbc.driver.OracleDriver");
            Properties props = new Properties() ;
            props.put( "user" , "test_schema") ;
            props.put( "password" , "pwd") ;
            props.put( "oracle.net.CONNECT_TIMEOUT" , "10000000") ;
            props.put( "oracle.jdbc.ReadTimeout" , "2000" ) ;
            Connection conn = DriverManager.getConnection( "jdbc:oracle:thin:@10.0.1.9:1521:orcl" , props ) ;

通过环境变量设置

String readTimeout = "10000"; // ms
System.setProperty("oracle.jdbc.ReadTimeout", readTimeout);
Class.forName("oracle.jdbc.OracleDriver");
Connection conn = DriverManager.getConnection(jdbcUrl, user, pwd);

注意需要在connection连接之前设置环境变量

tomcat jdbc pool

一般我们不直接使用jdbc connection，而是使用连接池。由于tomcat jdbc pool是springboot默认使用的数据库连接池，这里就讲述一下如何在tomcat jdbc pool下设置。

spring.datasource.tomcat.connectionProperties=oracle.net.CONNECT_TIMEOUT=10000;oracle.jdbc.ReadTimeout=60000

注意，这里是分号分隔，单位是毫秒，这里可以根据各自的情况配置前缀(tomcat jdbc连接池的话，默认是spring.datasource.tomcat)，可以自定义，比如

    @Bean
    @Qualifier("writeDataSource")
    @ConfigurationProperties(prefix = "spring.datasource.write")
    public DataSource writeDataSource() {
        return DataSourceBuilder.create().build();
    }

假设你这里是自定义了prefix为spring.datasource.write，那么上述配置就变为

spring.datasource.write.connectionProperties=oracle.net.CONNECT_TIMEOUT=10000;oracle.jdbc.ReadTimeout=60000

oracle.jdbc.ReadTimeout如果没有设置的话，driver里头默认是0

oracle.jdbc.ReadTimeout

driver内部将该值设置到oracle.net.READ_TIMEOUT变量上

oracle.net.nt.TcpNTAdapter

    @Override
    public void setReadTimeoutIfRequired(final Properties properties) throws IOException, NetException {
        String s = ((Hashtable<K, String>)properties).get("oracle.net.READ_TIMEOUT");
        if (s == null) {
            s = "0";
        }
        this.setOption(3, s);
    }
    
    public void setOption(int var1, Object var2) throws IOException, NetException {
        String var3;
        switch(var1) {
        case 0:
            var3 = (String)var2;
            this.socket.setTcpNoDelay(var3.equals("YES"));
            break;
        case 1:
            var3 = (String)var2;
            if(var3.equals("YES")) {
                this.socket.setKeepAlive(true);
            }
        case 2:
        default:
            break;
        case 3:
            this.sockTimeout = Integer.parseInt((String)var2);
            this.socket.setSoTimeout(this.sockTimeout);
        }

    }

可用看到最后设置的是socket的soTimeout

实例

	@Test
	public void testReadTimeout() throws SQLException {
		Connection connection = dataSource.getConnection();
		String sql = "select * from demo_table";
		PreparedStatement pstmt;
		try {
			pstmt = (PreparedStatement)connection.prepareStatement(sql);
			ResultSet rs = pstmt.executeQuery();
			int col = rs.getMetaData().getColumnCount();
			System.out.println("============================");
			while (rs.next()) {
				for (int i = 1; i <= col; i++) {
					System.out.print(rs.getObject(i));
				}
				System.out.println("");
			}
			System.out.println("============================");
		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			//close resources
		}
	}

超时错误输出

//部分数据输出......
java.sql.SQLRecoverableException: IO 错误: Socket read timed out
	at oracle.jdbc.driver.T4CPreparedStatement.fetch(T4CPreparedStatement.java:1128)
	at oracle.jdbc.driver.OracleResultSetImpl.close_or_fetch_from_next(OracleResultSetImpl.java:373)
	at oracle.jdbc.driver.OracleResultSetImpl.next(OracleResultSetImpl.java:277)
	at com.example.demo.DemoApplicationTests.testReadTimeout(DemoApplicationTests.java:68)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
	at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
	at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:252)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:94)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
	at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
	at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:191)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:234)
	at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:74)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: oracle.net.ns.NetException: Socket read timed out
	at oracle.net.ns.Packet.receive(Packet.java:339)
	at oracle.net.ns.DataPacket.receive(DataPacket.java:106)
	at oracle.net.ns.NetInputStream.getNextPacket(NetInputStream.java:315)
	at oracle.net.ns.NetInputStream.read(NetInputStream.java:260)
	at oracle.net.ns.NetInputStream.read(NetInputStream.java:185)
	at oracle.net.ns.NetInputStream.read(NetInputStream.java:102)
	at oracle.jdbc.driver.T4CSocketInputStreamWrapper.readNextPacket(T4CSocketInputStreamWrapper.java:124)
	at oracle.jdbc.driver.T4CSocketInputStreamWrapper.read(T4CSocketInputStreamWrapper.java:80)
	at oracle.jdbc.driver.T4CMAREngine.unmarshalUB1(T4CMAREngine.java:1137)
	at oracle.jdbc.driver.T4CTTIfun.receive(T4CTTIfun.java:290)
	at oracle.jdbc.driver.T4CTTIfun.doRPC(T4CTTIfun.java:192)
	at oracle.jdbc.driver.T4C8Oall.doOALL(T4C8Oall.java:531)
	at oracle.jdbc.driver.T4CPreparedStatement.doOall8(T4CPreparedStatement.java:207)
	at oracle.jdbc.driver.T4CPreparedStatement.fetch(T4CPreparedStatement.java:1119)
	... 35 more

刚开始会有数据输出，但是到了某个resultSet的next的时候，报了超时(close_or_fetch_from_next)，这个超时指定的是当result.next方法触发新的一批数据的拉取(当一个fetchSize的数据消费完之后，接下来的next会触发新一批数据的fetch)之后在timeout时间返回内没有收到数据库返回的数据。

oracle的jdbc默认的fetchSize为10，也就是每个fetch，如果超过指定时间没接收到数据，则抛出timeout异常。

小结

jdbc的socketTimeout值的设置要非常小心，不同数据库的jdbc driver设置不一样，特别是使用不同连接池的话，设置也可能不尽相同。对于严重依赖数据库操作的服务来说，非常有必要设置这个值，否则万一网络或数据库异常，会导致服务线程一直阻塞在java.net.SocketInputStream.socketRead0。

如果查询数据多，则会导致该线程持有的data list不能释放，相当于内存泄露，最后导致OOM
如果请求数据库操作很多且阻塞住了，会导致服务器可用的woker线程变少，严重则会导致服务不可用，nginx报504 Gateway Timeout

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