Thread: AbstractJdbc2ResultSet.FAST_NUMBER_FAILED brings class loader leak

Hello, I'm working on fixing the issue "java.lang.OutOfMemoryError:
Metaspace" in the time of redeploy where running an web application on
Tomcat.

I have acquired a heap dump and found a weird Root GC reference which is
connected to org.postgresql.jdbc2.AbstractJdbc2ResultSet. The heap dump
shows that it saves a (intentionally constructed) NumberFormatException
in a private static final field FAST_NUMBER_FAILED and that field has
backtrace field which references a Servlet class that loaded by
WebappClassLoader.

Here's a screenshot of Eclipse Memory Analyzer:
http://www.nailedtothex.org/roller/kyle/mediaresource/2fabd2a0-10a3-4d45-b8c8-589763d15824

I think AbstractJdbc2ResultSet should stop saving a intentionally
constructed Exception in a static field because it creates a strong
reference to a class which invoked the database operation at the first
time regardless if it's loaded by WebappClassLoader. It will be a cause
of class loader leak.

[Steps to reproduce]

1. Put postgresql-9.3-1100.jdbc41.jar to $TOMCAT_HOME/lib
2. Put following element to $TOMCAT_HOME/conf/context.xml

    <Resource name="jdbc/PostgreSQLDS"
              url="jdbc:postgresql://localhost:5432/somedb"
              driverClassName="org.postgresql.Driver"
              username="postgres"
              password="***"
              auth="Container"
              type="javax.sql.DataSource"
              maxActive="20"
              maxIdle="5"
              maxWait="10000"/>

3. git clone https://github.com/lbtc-xxx/jdbc-servlet
4. cd jdbc-servlet; mvn clean package
5. deploy the WAR
6. visit http://localhost:8080/jdbc-servlet-1.0-SNAPSHOT
7. undeploy and deploy the WAR several times (keep your JVM running)
8. acquire heap dump and load it with Eclipse Memory Analyzer

[My environment]

* postgresql-9.3-1100.jdbc41.jar
* Tomcat 8.0.18
* Oracle JDK 8u60
* PostgreSQL 9.3.4

Thanks.

Kohei,

Thanks for the detailed testcase.

I've filed a pull request to fix the problem:
https://github.com/pgjdbc/pgjdbc/pull/397


Vladimir

Hi Vladimir,

Thank you for the fix, I've just confirmed that the class loader leak
has been fixed. Now all of the WebappClassLoaders are garbage collected
cleanly.

Regards,
Kohei

On 10/13/15 0:58, Vladimir Sitnikov wrote:
> Kohei,
>
> Thanks for the detailed testcase.
>
> I've filed a pull request to fix the problem:
> https://github.com/pgjdbc/pgjdbc/pull/397
>
>
> Vladimir
>
>