We host a service (servlet running on jboss), which receives something like 5-6 requests per second. Every request needs to connect to mysql through hibernate. Most of our requests do selects, with an insert/update every 5th/6th request. The hibernate mysql connection gets timed out after mysql connection time out period (8 hours). Even after having a request pinging our service, every hour, the mysql connection sometimes gets randomly disconnected after a day or so. We want hibernate to reconnect in case the connection is disconnected due to any reason, and maintain the number of connections we want it to.
We tried C3P0, with the following configuration:
<property name=c3p0.acquire_increment>1</property> <property name=c3p0.idle_test_period>3600</property> <property name=c3p0.max_statements>0</property> <property name=c3p0.min_size>1</property> <property name=c3p0.timeout>3605</property> <property name=hibernate.c3p0.preferredTestQuery>select 1;</property> Hibernate connection_pool size was set to 1.
This made the timeout/disconnect problem go away. But we started facing another problem. Long waits. Normally the request serve time for us is 2-3ms for select and 40-50ms for insert/update. But, after using the above C3P0 configuration, we saw that every request completing after an update was taking more than a minute and sometimes even 4-5 minutes! From our logs, it seemed that randomly a select request would get stuck and will be able to complete only after an update request was received and served.
Above problem goes away if we remove the C3P0 config. Can somebody suggest what we might be doing wrong?
Here is the complete hibernate config for reference:
<?xml version='1.0' encoding='utf-8' ?> <!DOCTYPE hibernate-configuration PUBLIC '-//Hibernate/Hibernate Configuration DTD 3.0//EN' 'http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd'> <hibernate-configuration> <session-factory> <property name='connection.driver_class'>com.mysql.jdbc.Driver</property> <property name='connection.url'>jdbc:mysql://xxx.xxx.xxx</property> <property name='connection.username'>xxx</property> <property name='connection.password'>xxx</property> <property name='connection.pool_size'>1</property> <property name='dialect'>org.hibernate.dialect.MySQLDialect</property> <property name='current_session_context_class'>thread</property> <property name='hibernate.cache.use_query_cache'>false</property> <property name='hibernate.cache.use_second_level_cache'>false</property> <property name='show_sql'>true</property> <!-- Transaction isolation 2 = READ_COMMITTED --> <property name='connection.isolation'>2</property> <property name='connection.autocommit'>true</property> <!-- configuration pool via c3p0--> <property name='c3p0.acquire_increment'>1</property> <property name='c3p0.idle_test_period'>3600</property> <!-- seconds --> <property name='c3p0.max_size'>1</property> <property name='c3p0.max_statements'>0</property> <property name='c3p0.min_size'>1</property> <property name='c3p0.timeout'>3605</property> <!-- seconds --> <property name='hibernate.c3p0.preferredTestQuery'>select 1;</property> </session-factory> </hibernate-configuration>
I’d recommend abandoning C3P0 and using the JNDI naming service and connection pooling that JBOSS provides.
Be sure that you are closing connections properly and returning them to the pool. Connect, query, close, all in the narrowest scope possible. No connection should be hanging around for eight hours.
Some more links might be pertinent: http://www.hibernate.org/117.html and http://www.informit.com/articles/article.aspx?p=353736&seqNum=4 regarding Hibernate and closing connections, and this MySQL bug that cites problems with MySQL, Hibernate, and connections: http://bugs.mysql.com/bug.php?id=10917