Connection hangs after time of inactivity

Question

In my application, Spring manages connection pool for database access. Hibernate uses these connections for its queries. At first glance, I have no problems with the pool: i

Answer 1

We solved problem with similar symptoms which also turned out to be caused by a firewall.

We were able to work around the problem by changing the testWhileIdle connection pool property which prevents the connection from going idle and from the firewall shutting down the connection. See Apache commons dbcp BasicDataSource. Here is an exert from the configuration file, persistentce-context.xml that fixed the problem:

<property name="testWhileIdle">
  <value>true</value>
</property>
<property name="minEvictableIdleTimeMillis">
  <value>600000</value>
</property>
<property name="timeBetweenEvictionRunsMillis">
  <value>600000</value>
</property>

Most likely we only need to add the testWhileIdle (false by default), but added the other two properties for good measure.

In our case, here are some of the logs which we were seeing. Notice in this debug logs, it would take 16 minutes to open the connection before the connection could be used and this is what caused everything to hang. There were no errors which made it hard to track down.

09-06-13 @ 16:36:34 [DEBUG] HibernateTransactionManager - Preparing JDBC Connection of Hibernate Session [org.hibernate.impl.SessionImpl@db17ab]
09-06-13 @ 16:36:34 [DEBUG] ConnectionManager - opening JDBC connection
09-06-13 @ 16:52:00 [DEBUG] DataSourceUtils - Setting JDBC Connection
09-06-13 @ 16:52:00 [DEBUG] JDBCTransaction - begin
09-06-13 @ 16:52:00 [DEBUG] JDBCTransaction - current autocommit status: true

Answer 2

you have to add some parameters in your DataSource:

more important add testOnBorrow and validationQuery

Answer 3

Check the config of your pool implementation. Usually, it's Apache DBCP which has a timeout for each connection after it will close it.

In your code, you shouldn't keep connections around. Get one, use it, close it immediately. The pool will make sure that this doesn't cost too much.

Answer 4

I've had problems like this before when the database is on a seperate box and there's a firewall in between which is set to timeout idle connections.

In some circumstances the firewall cuts off the connection in such a way that the JDBC end doesn't detect, and attempting to use it results in an indefinite block.

In my case it was a custom connection pool which sent a test query down the connection before returning it from the pool. I configured this test query to have a timeout (using Statement.setQueryTimeout) so that it didn't block indefinitely.

Answer 5

One way to resolve idle time out issue is to have dual connection pools, one is active and other one is standby (no connections created yet). Have a timer with trigger time much less than FIREWALL_IDLE_TIMEOUT and switch between connection pools. I tried this and ITS WORKING.