Performance incorporate with JReport

Hi,

Currently I'm using postgresql v8.1.3 and the latest jdbc.

I try to open a JReports' report and the time taken to completely open the
report is 137453ms.
Then I open the same report but this time I connect to postgresql v7.2.2
but the completion time is even faster than connect to postgresql v8.1.3
which took 15516ms to finish.

I try many times and the result is still the same.

So I think it might be compatibility problem between JReport & Postgresql
8.1.3 so i add in 'protocolVersion=2' in the connection string.
Then i open the same report again and this time it just as what i expected,
the execution time for the report become 6000ms only,
it is 20x times faster than previous test without 'protocolVersion=2'
option.

May I know what is the reason of this?
Is it because of the compatibility between JDBC driver with JReport?

Thanks!