NHibernate and hilo generator: how to design key

2018-06-06 02:51:08

I'm about to switch some of my entities from identity to hilo id-generator.

I'm don't have a clue how the tables holding the next-high values should be designed.

should I use a single table for all entities, or for a group of related entities?

should I use another table for each entity?

should I use a single table with another row or column per entity?

Are there any best practices? What needs to be considered? Are there any pros or cons for any of the approaches?

I don't think there's a single "best" practice, but it's important to understand how HiLo works:

The table hilo generator is designed for databases which do not support sequences, which are a more natural fit for this task.

The Hi value for a class is retrieved and updated the first time you save an instance of that class, or when you run out of Lo values.

A different Hi value is used for each class.

So, you'll have to consider at least two variables:

Contention. You might improve performance a little bit by using separate tables

Range. With a very big database, you have a bigger risk of eventually running out of Hi values.

After considering that, it's just a matter of taste.

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