Connection Problems!

Dear all,

I have an problems with my postgresql database. My Database is 8.2.5
and size is ~10GB with a lot of simple select,update,insert statement
using indexes.
My programs was built base on Java Environment using JDBC. In normal,
there is no problem, the program run well, all transaction is complete,
but sometimes, it dropped out connection in the middle of transaction
and it threw this log:

"java.lang.Exception: DB Error:
org.postgresql.util.PSQLException: An I/O error occured while sending to
the backend."

In server's log, there isn't any notice about that errors. That
transaction contain about 3 insert query to 3 table and 1 update to
another table.
Besides, I'm sure that in my code, I've already set Autocommit to
false. But when it dropped connection as that case, it was still
insert/update into table, of course the remain query wasn't executed.

Do you know why? Or do you have any suggestion for me?

Thanks so much,
Best Regard,

Đỗ Ngọc Trí Cường.