How to choose the id generation strategy when using JPA and Hibernate
I was going through Id generation section of the Hibernate reference guide and "java persistence with Hibernate"
There are quite a few options available with Hibernate and JPA combined.
I was looking for a further documentation on how to choose the specific id generation strategy.
I am also looking for tipping points.
For example, hilo strategy is expected to reduce contention. I am assuming there must be a trade off associated with this choice.
I want to be educated about the trade offs.
Is there any literature available?
Answer
The API Doc are very clear on this.
All generators implement the interface org.hibernate.id.IdentifierGenerator. This is a very simple interface. Some applications can choose to provide their own specialized implementations, however, Hibernate provides a range of built-in implementations. The shortcut names for the built-in generators are as follows:
increment
generates identifiers of type long, short or int that are unique only when no other process is inserting data into the same table. Do not use in a cluster.
identity
supports identity columns in DB2, MySQL, MS SQL Server, Sybase and HypersonicSQL. The returned identifier is of type long, short or int.
sequence
uses a sequence in DB2, PostgreSQL, Oracle, SAP DB, McKoi or a generator in Interbase. The returned identifier is of type long, short or int
hilo
uses a hi/lo algorithm to efficiently generate identifiers of type long, short or int, given a table and column (by default hibernate_unique_key and next_hi respectively) as a source of hi values. The hi/lo algorithm generates identifiers that are unique only for a particular database.
seqhilo
uses a hi/lo algorithm to efficiently generate identifiers of type long, short or int, given a named database sequence.
uuid
uses a 128-bit UUID algorithm to generate identifiers of type string that are unique within a network (the IP address is used). The UUID is encoded as a string of 32 hexadecimal digits in length.
guid
uses a database-generated GUID string on MS SQL Server and MySQL.
native
selects identity, sequence or hilo depending upon the capabilities of the underlying database.
assigned
lets the application assign an identifier to the object before save() is called. This is the default strategy if no element is specified.
select
retrieves a primary key, assigned by a database trigger, by selecting the row by some unique key and retrieving the primary key value.
foreign
uses the identifier of another associated object. It is usually used in conjunction with a primary key association.
sequence-identity
a specialized sequence generation strategy that utilizes a database sequence for the actual value generation, but combines this with JDBC3 getGeneratedKeys to return the generated identifier value as part of the insert statement execution. This strategy is only supported on Oracle 10g drivers targeted for JDK 1.4. Comments on these insert statements are disabled due to a bug in the Oracle drivers.
If you are building a simple application with not much concurrent users, you can go for increment, identity, hilo etc.. These are simple to configure and did not need much coding inside the db.
You should choose sequence or guid depending on your database. These are safe and better because the id generation will happen inside the database.
Update: Recently we had an an issue with idendity where primitive type (int) this was fixed by using warapper type (Integer) instead.