Hibernate，什么是最有效的id生成策略？

Question

I need to insert many entities into the database via Hibernate. So, I want to find the most effective algorithm for Id generation.

Accordingly Hibernate Documentation exists four widely used generation strategies:

• IDENTITY
• SEQUENCE
• TABLE
• AUTO

I should use MySQL database, so I cannot apply SEQUENCE generation strategy. What about other strategies? What is the most efficient from performance point of view?

Answer 1

The best id generators in Hibernate are enhanced-table and enhanced-sequence , coupled with an appropriate optimizer, such as hilo . I have experience with enhanced-table + hilo , inserting over 10,000 records per second.

BTW the statement that "hilo needs an additional query per generated entity" is patently false: the whole point of the optimizer is to prevent this.

Answer 2

As you can't use SEQUENCE , and AUTO just automatically selects a supported generator algorithm out of the existing ones, you are left with IDENTITY and TABLE .

• TABLE : uses a hi/lo algorithm to efficiently generate identifiers of type long, short or int, given a table and column as a source of hi values. The hi/lo algorithm generates identifiers that are unique only for a particular database. -> Means an extra query per generated entity . (This is not true if you use optimizers. Unfortunately, using no optimizer generally is the default, if no optimizer was specified.)

• IDENTITY : supports identity columns in DB2, MySQL, MS SQL Server, Sybase and HypersonicSQL. -> Performance-wise, this is the way to go , the same way you would do without Hibernate normally. Database generated, almost no overhead.

There exist more Hibernate specific generators, but they won't beat performance-wise the database generated ID. (See 5.1.2.2.1. Various additional generators in your linked document.)