java - Hibernate 中的 beginTransaction 是否分配新的数据库连接？

Question

只是想知道在 Hibernate 中开始一个新事务是否真的分配了一个到数据库的连接？

我担心 b/c 我们的服务器会为收到的每个请求开始一个新事务，即使该请求不与数据库交互。我们发现数据库连接是一个主要瓶颈，所以我想知道我是否应该花时间缩小我的交易范围。

四处搜索，未能找到合适的答案。非常简单的代码在这里:

    SessionFactory sessionFactory = (SessionFactory) Context.getContext().getBean("sessionFactory");
    sessionFactory.getCurrentSession().beginTransaction();
    sessionFactory.getCurrentSession().setFlushMode(FlushMode.AUTO);

非常感谢!一个

Answer 1

根据 11.1. Session and transaction scopes 部分Hibernate 文档:

A SessionFactory is an expensive-to-create, threadsafe object, intended to be shared by all application threads. It is created once, usually on application startup, from a Configuration instance.

A Session is an inexpensive, non-threadsafe object that should be used once and then discarded for: a single request, a conversation or a single unit of work. A Session will not obtain a JDBC Connection, or a Datasource, unless it is needed. It will not consume any resources until used.

In order to reduce lock contention in the database, a database transaction has to be as short as possible. Long database transactions will prevent your application from scaling to a highly concurrent load. It is not recommended that you hold a database transaction open during user think time until the unit of work is complete.

现在，回答你的问题:

• 获取Session 不会立即获取连接(连接是延迟加载的)
• 但调用 beginTransaction() 将导致给定 Session 的连接加载
• 后续调用将重用相同的连接

查看 org.hibernate.impl.SessionImpl#beginTransaction() 并查看代码以获取更多详细信息。