Broken Pipe Issue in Hibernate

Hey guys, here is one of the many key issues which I was facing in one the web based java application on which I am currently working on. Here is the development environment.

• Java 1.6
• Struts 2
• Hibernate with C3p0
• Postgres
• Tomcat 6

Assuming database server & tomcat are both up an running and are on different machines. At any point if there is any network issues or for some reason database server goes down for few seconds, the c3p0/hibernate connection pool goes into bad state. And application keeps on throwing "Socket Exception" / "Broken Pipe" issue. And even if the database server comes up, it is not able to re-create the connection pool. The only solution to this issue is to re-start the tomcat server. There are other users who faced this issue with MySQL database.

There is key entry which was missing from my "hibernate.cfg.xml". Adding this entry resolves this issue.

<property name="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>

Along with the above I do have following properties in my application

<property name="hibernate.c3p0.min_size">5</property>
<property name="hibernate.c3p0.max_size">10</property>
<property name="hibernate.c3p0.max_statements">50</property>
<property name="hibernate.c3p0.timeout">1800</property>

I tested this setting and it works fine.
I just fixed my broken pipe !!! :)

Eclipse Memory Enhancements

Default Eclipse settings are optimal for machines running on 1 GB/low memory. So if you have a machine with high memory, you can use below settings to optimize performance. Add the following settings in eclipse.ini(residing in your eclipse home directory) file and start/restart the eclipse.

-Xmn128m
-Xms1024m
-Xmx1024m
-Xss2m
-XX:PermSize=128m
-XX:MaxPermSize=128m
-XX:+UseParallelGC

Thanks.

SQL Restriction In Hibernate Criteria Query

Here is an example to add a SQL Restriction in hibernate Criteria query.
Let's consider we have

• A Student.java entity
• A stored procedure in place which returns total marks obtained by a student in each subject.

public Class Student {
    private Integer id;
    private String name;
    .
    .
    //getters & setters methods
}

Assuming get_marks() stored procedure will result records in following format.

id	Maths	Enlish	Science
1	78	75	23
2	74	70	97

I want to list down the Students who has got more than 90 in Maths. Here goes the Hibernate Criteria query.

Criteria c = session.createCriteria(Student.class)
		.addSqlrestriction(" {alias}.id in (SELECT id FROM get_marks() WHERE maths_total > ? ) ", new Double(90.0), Hibernate.Double);

In above statement {alias}.id will refer to the id column of Student table. The above addSqlrestriction example shows the SQL restriction statement with only one parameter.
What if you have to pass multiple arguments?
In such cases you need to pass array of Objects & array of Type as second & third parameter to the addSqlrestriction(String, Object[], Type[]). And in SQL String have ? where ever argument is required, as shown in above example.

I hope this helps.
Thanks.