PostgreSQL JDBC驱动程序logUnclosedConnections不工作

Question

public static void main( String[] args ) throws Exception {

    Properties dbProps = new Properties();
    dbProps.setProperty( "user", "xxxxxxx" );
    dbProps.setProperty( "password", "xxxxxxxxxx" );
    dbProps.setProperty( "logServerErrorDetail", "true" );
    dbProps.setProperty( "logUnclosedConnections", "true" );
    dbProps.setProperty( "loggerLevel", "DEBUG" );

    Connection conn = DriverManager.getConnection( "jdbc:postgresql://xxxxx.xxxxx.xxx:xxx/xxxxx", dbProps );

    try {
        PreparedStatement pstmt = conn.prepareStatement( "select count(*) from xx.xx limit 10" );

        ResultSet rSet = pstmt.executeQuery();

        while ( rSet.next() ) {
            System.out.println( "count is " + rSet.getInt( 1 ) );

        }

    } catch ( Exception e ) {

        e.printStackTrace();
    }
}

count is 687
Sep 08, 2021 12:21:44 PM org.postgresql.Driver connect
FINE: Connecting with URL: jdbc:postgresql://xxxxx.xxxx.xxxx:xxx/xxxx
Sep 08, 2021 12:21:44 PM org.postgresql.jdbc.PgConnection <init>
FINE: PostgreSQL JDBC Driver 42.2.23
Sep 08, 2021 12:21:44 PM org.postgresql.jdbc.PgConnection setDefaultFetchSize
FINE:   setDefaultFetchSize = 0
Sep 08, 2021 12:21:44 PM org.postgresql.jdbc.PgConnection setPrepareThreshold
FINE:   setPrepareThreshold = 5
Sep 08, 2021 12:21:44 PM org.postgresql.core.v3.ConnectionFactoryImpl openConnectionImpl
FINE: Trying to establish a protocol version 3 connection to xxxx.xxxx.xxx:xxx
Sep 08, 2021 12:21:44 PM org.postgresql.core.v3.ConnectionFactoryImpl tryConnect
FINE: Receive Buffer Size is 65,536
Sep 08, 2021 12:21:44 PM org.postgresql.core.v3.ConnectionFactoryImpl tryConnect
FINE: Send Buffer Size is 65,536
Sep 08, 2021 12:21:44 PM org.postgresql.ssl.MakeSSL convert
FINE: converting regular socket connection to ssl

没有关于未关闭连接的报告。

public static void main( String[] args ) throws Exception {

    Properties dbProps = new Properties();
    dbProps.setProperty( "user", "postgres" );
    dbProps.setProperty( "password", "AuR0ra$dba#$" );
    dbProps.setProperty( "logServerErrorDetail", "true" );
    dbProps.setProperty( "logUnclosedConnections", "true" );
    dbProps.setProperty( "loggerLevel", "DEBUG" );

    Connection conn = DriverManager.getConnection( "jdbc:postgresql://devdbmaster.koncert.com:5499/dev_koncert_v10.5", dbProps );

    try {

        for ( int i = 0; i < 100; i++ ) {
            PreparedStatement pstmt = conn.prepareStatement( "select count(*) from cl.users limit 10" );

            ResultSet rSet = pstmt.executeQuery();

            while ( rSet.next() ) {
                System.out.println( "count is " + rSet.getInt( 1 ) );

            }

            Thread.sleep( 10 );
        }

    } catch ( Exception e ) {

        e.printStackTrace();
    }
    conn = null;
    System.gc();
    Thread.sleep( 1 );
}

按照@gus和@stephen C的建议，在system.gc()之前添加了conn=null；；

Answer 1

根据PostgreSQL JDBC驱动程序文档：

LogUnclosedConnections=Boolean

客户端可能会通过未能调用close()方法而泄漏connection对象。最终，这些对象将被垃圾收集，并调用finalize()方法，如果调用者自己忽略了关闭连接。终结器的使用只是权宜之计。

null

  rRet = null;
  pstmt = null;

  conn = null;
  System.gc();
  Thread.sleep(1);

system.gc()语句要求JVM运行GC。

thread.sleep(1)语句等待下一秒...以便JVM有机会在JVM结束之前运行连接终结器。

我在引号中说“工作”有几个原因：