检查数据库连接是否存活

Question

I'm writing stock quotes processing engine and receiving async notifications from postgresql database with pgjdbc-ng-0.6 library. I'd like to know if my database connection is still alive, so I wrote in thread's run() method

    while (this.running) {
        try {
            this.running = pgConnection.isValid(Database.CONNECTION_TIMEOUT);
            Thread.sleep(10000);
        } catch (SQLException e) {
            log.warn(e.getMessage(), e);
            gracefullShutdown();
        } catch (InterruptedException e) {
            gracefullShutdown();
        }
    }

I read isValid() declaration and it stated that the function will return false if timeout reached. However, isValid() just hangs indefinitely and run() is never exited. To create connectivity issues I disable VPN my application uses to connect to database. Rather rude way,but function must return false... Is this bug in driver or another method exists? I tried setNetworkTimeout() in PGDataSource , but without any success.

Answer 1

One of the possible handlings of this problem for Enterprise developers is to use existing threadPool to create a separate thread for submitting in Callable with test call() for DB (in case of Oracle it may be "SELECT 'OK' FROM dual" ), using statement object.execute('...') , (not executeUpdate , because it may cause the call to get stuck), and further using for example - future.get(3, TimeUnit.Seconds) .

Using this approach in a final call you need to catch InterruptedException for get() call. If Callable throws you set database availability as false, if not then true.

Before using this approach inside the Enterprise application you have to ensure you have access to application server threadPool executor in certain object and @Autowire it there.