Explanation of NHibernate HiLo

Question

I\'m struggling to get my head round how the HiLo generator works in NHibernate. I\'ve read the explanation here which made things a little clearer.

My understanding

Answer 1

I believe your understanding is more or less correct. The max_lo parameter is simply used to determine the number of Ids available for any given Hi value.

My best guess is that NHibernate's default max_lo value is 32768. Thus a Hi value of 1 would start your Ids at 32768 and run you right up to 65535. A Hi value of 2 would start at 65536 and run up another max_lo Ids.

Basically you use the max_lo value to control Id fragmentation. 32768 is likely not the optimal value for every situation.

It is important to note however that this only works within the scope of a SessionFactory. If you are stopping/starting your application and reinitializing the SessionFactory a whole bunch, it's going to increment the Hi value upon startup anyway and you're going to see your Ids jump pretty quickly.