EclipseLink和H2策略= GenerationType.AUTO

Question

I'm using EclipseLink and H2 and I have set the strategy to

strategy = GenerationType.AUTO

because IDENTITY strategy didn't work (it tried to insert a NULL id and failed).

Now I don't know what the AUTO type uses but it seems to work, the ids given are however a bit random while I'd like them to start from 1 and increase at steps of 1 when possible.

JPA however seems to insert 1,51,52,101,151 which is a little too random and I consider it a waste of numbers. Even if it wasn't a waste (for instance because JPA also used the missing numbers between the gaps) I would like for the ids to be increasing and not random!

Any suggestion on how to set it so?

Answer 1

The default pre-allocation size in JPA is 50, you can set the allocationSize to change this increment to 1, although I would not recommend this, as this will make your performance much worse.

You still should not get holes such as this. Are you creating a new EntityManagerFactory for every request? (don't do this), or do you have multiple concurrent requests? are you using JTA?

IDENTITY does work with H2, ensure that you created your table with the correct IDENTITY type. AUTO is defaulting to TABLE sequencing. In general I do not recommend IDENTITY, as it does not support pre-allocation.