Multithreaded clients and Oracle JDBC-drivers?

Question

Are the thin and OCI8 drivers for Oracle multithreaded? (I know they're thread safe)
I.e. Can many threads share the same Connection object (and statement objects) to do their requests without the requests being serialized to the DB?
Sun's javadoc of package java.sql says:
We require that all operations on all the java.sql objects be multi-thread safe and able to cope correctly with having several threads simultaneously calling the same object.
Some drivers may allow more concurrent execution than others. Developers can assume fully concurrent execution; if the driver requires some form of synchronization, it will provide it. The only difference visible to the developer will be that applications will run with reduced concurrency.
For example, two Statements on the same Connection can be executed concurrently and their ResultSets can be processed concurrently (from the perspective of the developer). Some drivers will provide this full concurrency. Others may execute one statement and wait until it completes before sending the next.
One specific use of multi-threading is to cancel a long running statement. This is done by using one thread to execute the statement and another to cancel it with its Statement.cancel() method.
Restated again for Oracle; Will threads run concurrently when using the same connection and statements, or will the calls be serialized?

Answer 1

In the connection pool, I specified:
user
password
url
In the deployment tool (Sun Java Appl. Server 8 BE Update 1), I specified the "Resource Reference" for the EJB. This leads to the following entries in sun-ejb-jar.xml:
<res-ref-name>jdbc/pdisasdb</res-ref-name>        
   <jndi-name>jdbc/pdisasdb</jndi-name>        
      <default-resource-principal>         
         <name>myname</name>          
         <password>geheim</password>        
      </default-resource-principal> 
</resource-ref> The strange thing is, that now it works without this entry - but I am not gaga, yesterday it doesnt...