I am using hibernate from within a managed weblogic server.
All my queries are read-only
Is it necessary to use
s = openSession();
t = s.beginTransaction();

<logic>

t.commit();
s.close();


or

s = openSession();
<logic>
s.close();

should suffice.
Does hibernate set autoCommit to false ?

If you're doing Read-Only, you won't need to start a transaction. Transactions are good for making sure all logic within that transaction is completed as a whole. Think of a Transaction as single unit of work.

Transactions are necessary to access database, "read-only" transaction is a transaction too, but it is not necessary to manage transactions if container manages this stuff.

so it is possible to NOT use t = s.beginTransaction(); when i make a read only?

See documentation about configuration and managed transactions, hibernate integrates with container and you can use declarative transaction demarcation. I prefer to use client transactions, it is more clear for me. Typical transaction demarcations is a transaction per request anyway. It is a web application, is not it ? If it is a web application then demarcate transactions in filter or in "controler" implementation, you can change filter to use local (hibernate transaction API) or remote transactions ("UserTransaction" from JTA API). Do not use transaction demarcation in transaction processing code (transaction is per usecase and the same method can be used in many places), but same rules are valid for all transactions. Databases have "readonly" transaction concept ("SET TRANSACTION READONLY"), you can set this transaction attribute in filter too, but you always need to demarcate transactions in some way to avoid random data (it can happen for "readonly" operations with wrong transaction demarcation too )