Setting an isolation level

Setting an isolation level
Every JDBC connection to a database is in the default isolation level of the DBMS—
usually read committed or repeatable read. You can change this default in the
DBMS configuration. You may also set the transaction isolation for JDBC connec-
tions on the application side, with a Hibernate configuration option:
hibernate.connection.isolation = 4
Hibernate sets this isolation level on every JDBC connection obtained from a
connection pool before starting a transaction. The sensible values for this option
are as follows (you may also find them as constants in java.sql.Connection):
■ 1—Read uncommitted isolation
■ 2—Read committed isolation
■ 4—Repeatable read isolation
■ 8—Serializable isolation
Note that Hibernate never changes the isolation level of connections obtained
from an application server-provided database connection in a managed environ-
ment! You can change the default isolation using the configuration of your appli-
cation server. (The same is true if you use a stand-alone JTA implementation.)
As you can see, setting the isolation level is a global option that affects all con-
nections and transactions. From time to time, it’s useful to specify a more restric-
tive lock for a particular transaction. Hibernate and Java Persistence rely on
optimistic concurrency control, and both allow you to obtain additional locking
guarantees with version checking and pessimistic locking.