CODEWITHSUNDEEP
nhibernatedatabase-designhilo
Stefan Steinegger
Stefan Steinegger

Reputation: 64658

NHibernate and hilo generator: how to design key-tables?

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.

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

Upvotes: 8

Views: 1861

Answers (1)

Diego Mijelshon
Diego Mijelshon

Reputation: 52753

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.

Upvotes: 3

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