Hibernate Learning (iv) Hibernate cache & Snapshot

caching: High efficiency

Hardware CPU cache memory for hard disk cache

IO Stream caching for software

Hibernate's first-level cache is also designed to operate the database efficiently.

Proof of a slow existence:

Person p=session. Get (Person.class, 1);

Person P1=session.get (person.class,2);

Person P2=session.get (person.class,3);

System.out.println (P=P1);

The console output is:

SELECT * from the person where id=1;

True

Caching principle:

Snapshot

When the code changes to:

Note: The name value of the first data in the original Database person table is "Zhang San"

Person P=session.get (person.class,1);

P.setname ("Zhangsan");

P.setname ("Zhang San");

After execution, the console appears as

SELECT * from the person where id=1;

View the database in the person table with a data ID of 1 name= "Zhang San"

This applies to the snapshot of hibernate:

Increase efficiency: 1. Improve query efficiency (caching principle) 2. Reduce unnecessary modification statement send (snapshot)

To see Hibernate object status from the cache:

1. Transient status: No ID, no in session cache

2. Persistent status: With ID, in session cache

3. Free/Managed Status: There is no ID in the cache

A deeper understanding of the snapshot: The following code intercepts some of the main code in the test method

.........

Person P=new person (); Instantaneous state

P.setid (1); Free State, with ID not cached in session

Session.update (P); Persistent state, with ID cached in session

Person P=session.get (Person.class, 1);

Tx.commit ();

.........

=new person in person P (); Set a breakpoint, debug mode to execute the view console in the SQL statement display

Until run to person p= session.get (person.class, 1);  Console output update person set name=?   Age=?     Sex=? where id=?

This behavior occurs because the object is persisted through update, and the object is not put into a snapshot by the Get method.

When the object commits, the Nineth step is executed: The object is compared to the objects in the snapshot, and if it is not the same, the UPDATE statement is executed; The UPDATE statement is executed without a snapshot

Hibernate Learning (iv) Hibernate cache & Snapshot